Medical Experimentation on Animals
I
MODERN medicine depends so largely upon animal experimentation, that, without it, the healing art would still remain a mere mixture of empiricism and superstition, as is the case in China to-day. Both the moral and legal codes forbid experimentation on human beings without their own consent; and as the results obtained from cold-blooded animals are commonly inapplicable to ourselves we are obliged to conduct our researches on the bodies of our nearest relatives, — the warm-blooded lower animals. The ancients derived much of their medical knowledge from this source: we find the great Galen conducting extensive and profitable researches on apes and dogs. In the Middle Ages, however, the deadening influence of scholasticism discouraged animal experimentation; we are therefore not surprised to learn that for over a thousand years medicine stood still.
With the great intellectual awakening that characterized the so-called Renaissance, the teachings of the ancients were felt to be insufficient. Vesalius and others studied the structure of the human body as thoroughly as the prejudices of the time permitted; progress in the science of physiology began; surgery threw off its old association with the barber’s trade. In the seventeenth century, the invention of the microscope led to the assiduous study of our more minute structure. Nevertheless, if investigators had limited themselves exclusively to the consideration of the human body, alive and dead,healthy and diseased, the science and practice of medicine could not have continued to advance. This limitation restricts us too closely to actual conditions; it excludes all such as are hypothetical or artificial. The voluntary submission of a human subject for medical experimentation is rarely obtainable, though a number of physicians, from grand old John Hunter to our own brave Lazear, have offered their persons and risked their lives in the interests of medical science. Such instances of noble self-devotion are infrequent, and should remain so; they are justified only by the direst necessity. It is indefensible to experiment upon men, when information equally, or almost equally, worthy of confidence can be derived from the lower animals.
The appreciation of this rather elementary moral principle has led to the marvelous progress in medicine that is one of the triumphs of our age. I would not pretend that the science and practice of medicine — two very different things, by the way — are anywhere near perfection; but it is true that the greater part of the physical ills of humanity are to-day under the physician’s control, while only a very few remain altogether beyond our reach. Indeed, Metchnikoff, one of the ablest investigators on animals, thinks that there is a prospect of a fairly successful fight to defer the approach of man’s greatest enemy, old age.
Cruelty to animals is abhorrent to modern civilization; it lowers man to the level of the brute, and, in the case of warm-blooded animals, it is punishable at law. This characterization applies, however, solely to wanton cruelty, for even an act of true kindness may involve cruelty. In this connection it is my duty to do what should be unnecessary, and is certainly highly distasteful to me as a physician, but which seems to be demanded by some of our critics, namely, to remove the widely prevalent impression that familiarity with suffering breeds callousness. The best evidence against this impression is the conduct of the medical profession itself.
Our critics must remember that the only notice we take of suffering is to try to assuage it, that our most distressing experience is to witness suffering which cannot be relieved, and that we take as much satisfaction in banishing pain as in saving life. As for our supposed indifference to animal suffering, merely to state that the infliction of pain actually interferes with the usefulness of most animal experiments, will convince well-meaning but uninformed persons that, whenever possible, operations on animals are conducted under the same methods of anæsthesia that are applied to human beings.
We destroy lions and wolves, not to speak of mice and rats, merely because they attack our lives or property whenever they can. Their interests are opposed to ours, and that, seals their fate. The investigations upon animals which tend to subserve our interests, at the expense of theirs, should be considered from the same point of view. It may seem harsh, but it is only logical to characterize the man who subordinates the health and happiness of his fellow men to the comfort of some rabbits and dogs, as an enemy to mankind. The old Roman law justly regarded this as the basest of all crimes.
II
Many well-intentioned persons, who earnestly desire the limitation of vivisection to what is actually necessary, believe that a restriction to practical ends would fulfill the ideal of both minimizing cruelty and fostering medical progress. These people are unaware of the fact that there are two sides to medicine, namely, medical science, or rather the medical sciences, and the medical art, commonly called the practice of medicine and surgery.
It is a philosophic principle that a pure science cannot be practical, but deals solely with observed facts, theories, and hypotheses. The application of a science to practical ends is more properly called a useful art. In the medical sciences we study the structure of the human body, its composition, its functions in health, the impairment it suffers from disease, and the remedies for disease. In the practice of medicine we do not treat diseases but patients. The practicing physician is confronted with a sick man, not with an abstract question. He endeavors to apply his scientific knowledge to the aid of his patient, but he does not regard him as a scientific problem. This point is misunderstood by many people, and has led to the unwarranted and scandalous assertion that hospital patients are frequently the objects of experiments. The exact contrary is true: with a few unavoidable exceptions, no procedure is tried upon a human being that has not been proved harmless to the lower animals. The misdirected energies of the ‘ anti-vivisectionists ’ merely tend to increase the number of exceptions to this rule.
Physiology, which deals with the functions of the healthy body, is, like anatomy, fundamental to the medical sciences. Many of the deficiencies of modern medicine are due to gaps in our physiological knowledge, while much of our progress in treatment is the result of recent advance in this science. As examples, I may mention the modern methods of dieting, exercise, change of climate, and regulation of regimen in its broadest sense. I must not, however, ignore the vast improvement in medication with drugs, which is a consequence of our advance in what physicians call pathological physiology, meaning thereby the perverted physiology of the diseased body. We are learning to appreciate the various compensations, whereby a diseased organ is more or less replaced by one that is still sound; and also that great compensatory scheme, which enables a generally diseased body to remain not only alive, but even fairly efficient. One can see how this knowledge may be utilized to the advantage of what the insurance companies call impaired risks; it is safe to say that the lease of life of sufferers from diabetes, heart disease, and Bright’s disease, has been doubled within recent years.
The ancient physicians believed that the arteries contained air; that, indeed, is the meaning of the word artery. Galen proved that they contained blood, by cutting them in living animals; there was no other way of settling this fundamental fact, for, in the dead body, the arteries are quite empty. The circulation of the blood was demonstrated by Harvey through experiments on dogs. The capillaries, connecting the arteries and veins, were first seen by Malpighi in the lung of a living frog. It is evident that these observations could not have been made in any other way. The nineteenth century has greatly advanced our knowledge of the wonderful pumping and pipe-line system within our bodies. We now know the speed of the blood-current, its volume and its force, and have a fair idea of the nervous mechanism which controls it. To study these problems, it has been necessary to attach the most varied physical apparatus to the heart and blood-vessels of living animals; it will, however, reassure the reader to learn that to be of real value these experiments must be conducted under anæsthesia. Without them, we should not have the faintest clue to the successful treatment of patients suffering from heart disease.
In the study of the physiology of respiration, little can be learned from the observation of living and healthy men, that does not need corroboration through experiments on animals. As instances, I may mention the demonstration that the aeration of the blood takes place in the capillaries of the lungs; the apparently simple facts that we cannot live without oxygen, and that air which has been once breathed is poisonous; the action of the muscles of respiration, and the nerve-supply which directs them. Not one of these points could have been investigated save by the sacrifice of a number of animals. The whole subject of artificial respiration, so important in the resuscitation of asphyxiated human beings, has been and still is in process of discovery from experimentation on the lower animals. I need only call attention to the newly proposed methods of resuscitation from electric shocks, which would deserve no attention whatever if they did not appear successful when applied to animals.
Proceeding to the study of digestion, let us begin by noting that only its earlier and less important stages are accessible in the intact bodies of men or animals; even so we must employ the extremely uncomfortable stomach-tube, which cannot be used very frequently without starving the subject under investigation, and yields at best but very fragmentary scientific results. The first really valuable investigations were made by Beaumont, about 1830, on a Canadian, one Alexis Saint-Martin, who suffered from a gunshot wound of the stomach, which had failed to close. Since then one or two other victims of this so-called gastric fistula have been studied, but such cases as these are far too rare to suffice for rapid scientific progress. It has therefore become necessary to perform similar experiments and investigations on dogs, whose stomach-digestion is very much like ours. These dogs, fitted with an artificial external opening in the stomach, through which food may be poured in and withdrawn, feel no more pain than did Beaumont’s Canadian, who enjoyed excellent health through years of observation.
These experiments have shown how the gastric juice begins to flow at the very sight of food; how the food is changed in the course of its sojourn in the stomach; how some substances favor digestion, and others interfere with it; how the stomach moves, and how it is finally emptied. Without actual observation we should have to guess at these and nearly all the other phenomena of stomach-digestion.
The digestion which goes on in the intestine is far more important than that in the stomach itself, and it is hardly necessary to inform the reader that we should know absolutely nothing about it unless we had studied it in animals, The same is true of the functions of the great digestive glands, the liver and the pancreas; likewise of the great solar plexus of nerves which controls the whole apparatus. In this vast department of physiology new facts are continually coming to light, as operations on animals become more and more specialized.
In passing, I should refer again to one fact which is often disregarded. Digestive experiments on animals which are suffering pain are quite unsatisfactory; it is needless to add that pain had to be inflicted to prove this point, which otherwise would merely be suspected.
Closely connected with the above experiments are those which instruct us in the subjects of nutrition and of tissue-change. We have learned how to grow fat and how to reduce weight, what it means to be hungry or to be satiated. Some of these studies can be carried out on the human subject, but those suspected of being dangerous to health must be made on the lower animals. It is natural, therefore, that some of the dogs in the laboratories will be overfed and others half-starved; this is inevitable.
It is highly significant of the dense ignorance of our grandfathers, that so fantastic and absurd a system as Gall’s phrenology was accepted even by some physicians as a likely explanation of brain physiology; I am afraid that many intelligent persons still believe in phrenology. Through experiments on the brains of living animals we have learned which portions of the brain control the muscles, which experience the sensation of pain, which regulate the body’s temperature, the act of breathing, the senses of sight and hearing, and which govern the other bodily functions. Most of these investigations necessarily consisted in irritating or removing portions of the brain, and some very few forms of research had inevitably to be conducted without anæsthesia. To understand what pain is, we unfortunately must cause it. It is a most instructive fact, that those portions of the brain about which we know least are the very ones that are poorly developed in the lower animals; progress has been arrested chiefly because animal investigation is no longer available. We must recall, too, that the previous experiments on cold-blooded animals, whose brain-functions are of an altogether lower type than ours, had yielded little that could be applied practically, though extremely important and interesting. It was only when dogs and, more especially, our still nearer relatives, the apes, were drawn into the experimental field, that we really began to find out what was going on in our own brains. I may add that the observation of the diseased human brain, both at the bedside and post mortem, has always been extremely fragmentary and unsatisfactory.
As with the brain, so with the nerves: most of our knowledge is derived from experiments on the lower animals. It has been the fashion among the antivivisectionists to reserve especially vehement abuse for the great Magendie, who laid the very foundations of our present, still somewhat incomplete, knowledge of nerve-functions, nervetracts, and nerve-regeneration. It is true that Magendie’s work involved the infliction of a great deal of pain, but we should, in simple justice, remember that anæsthesia was unknown in Magendie’s day, and one of the many results obtained in this field of work is the demonstration that the sensations of man are far keener than those of the lower animals. As sensation, including that of pain, is purely a brain-function, which may be entirely abolished by stupefying the cells of the gray matter with an anæsthetic, it is evident that acuteness of sensation is apt to increase with the complexity of the brain-structure. This is unquestionably highest in man, and higher in the upper than in the lower races; thus the inferior races plainly show that they feel pain less than do the pampered products of civilization. On the average, the endurance of pain will vary in inverse proportion to its severity; if we eliminate the influence of self-control, that deference to convention and public opinion called stoicism, the demeanor of the victim of a pain is a fair guide as to its intensity.
III
It is scarcely necessary for me to remind the reader of the indebtedness of modern medicine to the science of bacteriology, that branch of natural history which treats of the minute germs known as bacteria. The difficulties encountered in studying bacteria will be appreciated, when we consider that millions of the larger germs can live and flourish in a single drop of milk, whereas the smallest, under the most powerful microscope, appear like grains of fine dust.
Some of the ancient writers had suspected that certain infectious diseases might be caused by minute living organisms, but not until 1683, when Leeuwenhook had invented the microscope, could the bacteria even be seen. It was not until the middle of the nineteenth century, when Pasteur found ways of cultivating these germs, that the science of bacteriology may be said to have originated; it was only after 1880,when Koch showed how to cultivate them on solid media, that the science began to make rapid progress, and to revolutionize medicine. The reason for this lies in the fact that, to study bacteria, it is necessary to isolate them; they always occur mixed in their natural state, and of course remain mixed, if they grow in a fluid; it is easy to understand how the different species may be separated, if we cultivate them, like ordinary plants, on a solid surface.
Presently, the supposed germs of numerous infectious diseases were announced, and, as it had become comparatively easy to cultivate bacteria, isolate them, and study their peculiarities, it only remained to prove their responsibility for the diseases attributed to them. Let us remember that, in sick as well as in healthy persons, the harmless bacteria far outnumber those that are dangerous; of thousands of species, only a few dozen belong to the class called pathogenic, or diseaseproducing. At this stage of the science, Koch, most opportunely, laid down the three clauses of the following law: —
1. All cases of the disease must furnish the germ held responsible for it.
2. The germ must be cultivated so as to free it from mixture with other germs; that is to say, it must be obtained in pure culture.
3. Inoculation of germs, from the pure culture, must reproduce the identical disease.
Koch’s law has stood the test of thirty years. Whenever one of the three links in the chain is missing, we admit at once that the responsibility of the germ under investigation is uncertain, unless corroborated by strong circumstantial evidence; if two links are missing, the germ has only a questionable scientific standing, in any event. When all three clauses are satisfied, the case is complete, as has been proven repeatedly in other ways into which I cannot enter here; I mention the production of artificial immunity as one of them.
Koch’s third requirement presents the greatest difficulties to the bacteriologist. For example, when the tubercle bacillus had satisfied the first two, it was still manifestly undesirable to inoculate a human being with the pure culture, to see what would happen. Even the most scornful skeptic of Koch and his methods would have declined more or less politely to offer himself for this test.
Nothing therefore remained but to inoculate animals, many of which were known to suffer at times from tuberculosis. These experiments were completely successful: the animals became affected with unquestionable tuberculosis, and the germs, taken from them and cultivated, again reproduced the same disease in another series of animals. No one who has taken the trouble to inform himself on the subject now has the faintest doubt that this germ, and no other, is the cause of tuberculosis. Moreover, since the earlier experiments, further proofs have been supplied, also through investigations conducted on the lower animals.
If the laws of Germany had forbidden the inoculation of animals with germs that would make them sicken and die, Koch would have been compelled to pursue his ever-memorable researches in some other country, and that country would have received all the credit. If the whole world had been controlled by the anti-vivisectionists, consumptives to-day would not know how they became ill, nor how to guard the members of their families from becoming likewise infected; furthermore, the doctors, in many cases, would not even be able to make the diagnosis.
It may reassure tender-hearted readers to know that the injection of tuberculous material is no more painful than the familiar hypodermic, and that an animal sick from tuberculosis suffers less physical pain than the thousands of hapless human sufferers from this lingering disease, while of course it is free from the still more acute agony of the mind.
Tuberculosis also furnishes one of the most convincing arguments against one of the favorite stands of the antivivisectionists, namely, that, it should be made unlawful to repeat experiments intended merely to corroborate an already established fact. Fifteen years ago most of us took for granted that the tuberculosis of man was identical with that of cattle; this view prevailed only because the investigators had not made a sufficient number of experiments on animals. More frequent inoculations of human tuberculosis on cattle, and a more careful investigation of bovine tuberculosis, would long before have revealed what Theobald Smith showed in 1895, namely, that cattle tuberculosis is caused by a slightly different and far less dangerous germ. This leaves open the question whether the one form of germ may, under certain conditions, be transformed into the other; and, what is most important for us to know, whether the chief danger to man lies in the milk of infected cows or in the expectoration of infected persons. If Theobald Smith’s contention is established, we shall have to restrict the careless habits of consumptives with more firmness than ever, and relegate the supervision of cattle to a secondary, though still important position. In any case, all the work of studying the relation between human and bovine tuberculosis will have to be gone over again, and this research will have to be made, almost entirely, on animals.
It is curious, but true, that there is more confusion on this subject in England than anywhere else, and that England is the country where animal experimentation is most seriously hampered by law. Most unbiased observers feel that if the English physicians had depended less exclusively on the study of their patients and had given more attention to tuberculosis in animals, they would not have arrived at their present state of uncertainty.
Even more remarkable are the results of animal experimentation in diphtheria. The diphtheria bacillus was discovered by Loeffler in 1879, but its status was doubtful for some years: first, because of the number of other germs found in inflamed throats; secondly, because some harmless germs resemble it closely. But for Koch’s third law the whole matter would have remained doubtful. The guinea-pig, however, is remarkably susceptible to diphtheria, so much so that it is employed as a test for doubtful cases. Pure cultures from guinea-pigs that have died of diphtheria will in turn infect other guinea-pigs, and so on ad infinitum.
It was soon found that the diphtheria germ itself was not the most dangerous element in diphtheritic infection; it does not grow indefinitely, and usually remains exclusively at the site of infection, say the throat, rarely wandering through the body. It acts chiefly through the intense poison that it produces as a part of its tissue-change. The treatment of diphtheria at first made little progress because the only method that could be considered was disinfection of the throat. Unfortunately the throat is one of the most difficult parts of the body to disinfect; indeed, it is practically impossible to disinfect it thoroughly.
A new chapter in medicine was opened when a Spanish physician, Ferrán, in 1890, announced that he had succeeded in immunizing animals against diphtheria. His results were soon corroborated by other investigators. It has been learned that, in the case of certain infectious diseases, probably in the majority, an animal that survives the attack has formed the antidote to the poison of the disease within its own body; this is indeed the reason why it recovers. It has also been learned that if we infect a guinea-pig with diphtheria germs, we can combat the infection by injecting into the same animal the blood-serum of a guinea-pig that has recently recovered. The poison is called the toxin, the antidote the antitoxin, and it has been shown that the latter, in proper dosage, exactly neutralizes the former.
The younger members of the present generation cannot realize what a thrill of horror went through a household when the family physician made the diagnosis of diphtheria. Formerly, we stood almost helpless at the bedside of our diphtheria patients, and expected a fatal result in about half of the severe cases. To-day the death-rate of cases that are treated promptly is about one per cent. The only reason why there are still many deaths from diphtheria is that some persons — alas, some doctors also — have a prejudice against antitoxin, because they do not know what it is.
I doubt if there are enough guineapigs in the world to supply all our sick children with antitoxin. Fortunately, it has been found that horses give an ample supply, if we infect them with diphtheria germs. As a horse can give us about a thousand times as much blood as a guinea-pig, this wonderful remedy is not even very expensive. Nor does the horse suffer much from the occasional withdrawal of a moderate amount of blood; as a matter of fact, he is handled and fed very carefully, and has a decidedly easy life of it between tappings. It is a question whether he would object if he knew what was being done, and how many lives he was saving; his fellows in front of coalwagons surely find it harder to earn a living.
The story of the conquest of lockjaw is similar to that of diphtheria, the chief difference being that the antitoxin must be injected in advance, whenever we see a wound that looks as if it might contain the lockjaw bacillus. The treatment is therefore not quite so uniformly successful, and seems less effective than it really is, because we never know when we have saved a patient from death from this fearful disease: he simply remains as well as he was before, and no one can tell what might have happened if treatment had been omitted.
It is highly important to remember that the bacilli of diphtheria and tetanus are not at all injured by the antitoxin, but remain as malignant as they ever were; the antitoxin merely protects the infected person against their poison. Physicians have been very successful in protecting the nurses and relatives of diphtheria patients against this disease. A small protective injection of antitoxin absolutely guarantees them against this illness, even if their throats, as is apt to happen, become thoroughly infected with diphtheria germs.
As soon as animal experiments are no longer available, we go on from one defeat to another; the most that we can do is to employ prevention. A conspicuous instance is afforded by that blot on American civilization, typhoid fever. No doubt our fearfully long death-list from that filthy disease would diminish if we could infect some animal and obtain an antitoxin; the recently announced susceptibility of monkeys gives us careless Americans a ray of hope. Otherwise, our only recourse is the right kind of sanitation, which consists entirely in keeping human excrements out of our food and water.
IV
There are still many persons, including, I regret to say, some justices on the bench, who define the practice of medicine as the giving of drugs. Most of our patients still think that the most important thing they can get from us is a prescription, and they pay much more attention to the directions on a medicine bottle than to the verbal advice imparted in the doctor’s office. A large part of the community thinks that it might as well obtain its drugs at first hand from the druggist, without consulting a physician at all. This delusion has already slain its thousands, and will continue to fill early graves until the public learns better.
The truth is, that the administration of drugs is often the least important part of the aid we give our patients; we accomplish more through other means of treatment than with medicines. The progress in physiology, of which I have given a few feeble hints, is already so great that we know the human body far better than many of the things we put into it. Some of our best drugs are employed only as auxiliaries to other treatment, such as diet, exercise, baths, and massage, not to mention surgical operations. Only a few drugs are used for combating disease directly, and these are chiefly of the class called internal antiseptics; for instance, quinine.
The testing of drugs on animals is not always trustworthy, for even the highest, dogs and apes, often respond somewhat differently from man; this does not, however, argue for omitting the animal experiment when we wish to learn the properties and action of a new and unknown drug. Any one can imagine that it would be highly reprehensible to give a little-known, perhaps highly poisonous, substance to a man before trying it on the dog. Sometimes a dog will die from an overdose, because the action of a drug is still uncertain; it were better to lose a thousand dogs in this way than one patient.
Such delicate matters as the effect of a new preparation on the blood-pressure, the kidneys, the digestion, and the nervous system, have to be investigated in living animals. Be it remembered that we aim to have our experiments succeed, and are disappointed when they turn out badly. In the latter case, however, we have the satisfaction of knowing that the untoward result has not injured a human being.
There is a group of four related diseases, measles, scarlet fever, chickenpox, and small-pox, which agree in one not very flattering circumstance, namely, that we doctors do not know what causes them; we merely believe that they are caused by germs too small to be seen with our best microscopes. One fact, however, is worth noting: formerly, all four diseases were common; now, small-pox, the most dreaded of all, has become rare. The reason for this is as follows: —
In 1798, Jenner observed that persons who had come in contact with cattle suffering from a disease called cow-pox were thereafter immune to small-pox; we, of to-day, cannot adequately realize the vast significance of Jenner’s discovery. In the eighteenth century small-pox was, like measles, chiefly a disease of children; it killed about one tenth of the population, and permanently disfigured most of those who recovered, very few escaping altogether. We may declare with truth that the slow increase of the population of Europe, before the nineteenth century, was chiefly due to the ravages of the infectious diseases, of which smallpox was the worst. We may thus judge what a boon it was to humanity when the inoculation of cow-pox matter was found to protect human beings against small-pox for at least some years, whereas repeated inoculation, at moderate intervals, gave absolute and permanent protection. This form of inoculation is called vaccination; its compulsory introduction into everyday use has resulted in the almost total disappearance of small-pox from the more enlightened countries. In Germany, where vaccination and re-vaccination are strictly enforced, small-pox is almost unknown among the native population; in our southern and western states, where people are careless about vaccination, the disease is still quite common. We can truly measure a nation’s civilization to-day by the relative frequency of small-pox.
To supply vaccine lymph, we must keep a continuous series of calves affected with cow-pox. I am willing to admit that these animals would be more comfortable without this disease, but cannot persuade myself to weigh their trivial discomforts against the possible sufferings of thousands of human beings. The employment of calf-vaccine has been found necessary because vaccination from man to man involves the fearful risk of syphilitic infection. The only real dangers from calf-vaccine, namely, wound-infection and tetanus, can be guarded against by using very simple precautions; the imagined danger of contracting tuberculosis has been shown not to exist, for there is no such case on record.
One result of the practice of vaccination is, that small-pox is now much rarer in children than inadults, because most children have been vaccinated at least once. It is also much milder in adults than formerly, because one vaccination, in infancy, affords a partial protection ever after. It is, of course, wisest to repeat the operation on admission to school, and at long intervals later in life.
If only some animal could be found that is susceptible to measles and scarlet-fever, how much suffering would be spared our children!
The germ of cerebro-spinal meningitis was discovered by Weichselbaum in 1887, but was not generally accepted until about ten years later; its rôle had to be established on circumstantial evidence, for it did not conform to Koch’s third law : there was no animal known that would take the disease. We were therefore quite helpless when confronted with this terrible affliction, which killed at least three fourths of its victims and permanently maimed most of the remainder.
Little progress was made until it was discovered that monkeys could be infected with Weichselbaum’s germ. In the hands of Flexner, this discovery soon yielded wonderful results; a few years of study and experimentation on these animals have led to the production of a serum, similar to that employed in diphtheria, which cures ninetenths of the mild cases and many of the severest ones, if used early. Flexner’s scrum is only waiting for our next great epidemic, to show how wonderful it is.
The conquest of acute infantile paralysis promises to be similar. To be sure, this disease is not often fatal; it regularly, however, results in the lifelong paralysis of one or more limbs, thereby disabling the poor victim permanently. We all know a number of persons who limp about uncomfortably because they have had this disease in childhood. Flexner, and his assistants, have found that monkeys are also susceptible to the poison of this disease. These investigators are now seeking to prepare a curative serum, similar to that which is giving such excellent results in meningitis. Success will reduce the total number of our cripples by at least one half. Most remarkable of all, these experiments in infantile paralysis are succeeding regardless of the fact that the germ of this affection is still entirely unknown.
Let me add a few remarks on the terrible disease called hydrophobia,— the very existence of which is persistently denied by the dog-worshipers, notwithstanding that a number of persons die every year of this frightful malady. It is indeed fortunate that these deaths are not sufficiently common to convince the anti-vivisectionists; the reason for the low death-rate from hydrophobia is to be sought in a wonderfully successful method of treatment, somewhat similar to that used in tetanus, and based entirely on animal investigation. The person bitten by a mad dog is treated with injections consisting of preparations from the spinal cord of rabbits infected with hydrophobia. Owing to the slowness with which this disease develops, there is ample time for repeated injections of increasing strength. Thus the outbreak of the disease is entirely prevented, if there has been no great loss of time before treatment is begun; the only reason why people still die of hydrophobia is because misguided persons persuade them that it does not exist.
We owe the treatment of hydrophobia to Pasteur’s experiments on dogs and rabbits. The germ of this affection is still unknown. Better than treatment, of course, would be prevention, by muzzling all privately-owned dogs, and killing the mongrels that infest our streets. Owing to the loudvoiced protests of the dogs’ ostensible friends, nothing of the sort has been done; human beings still run the risk of a dreadful death, and hundreds of really valuable animals are lost through being bitten by rabid curs.
The most mysterious and dreaded disease known to mankind is cancer, and it is becoming more frequent as other diseases diminish. Some of the increase of cancer is undoubtedly due to the falling-off in deaths from the diseases of childhood and youth: cancer, being a disease of later life, obtains more material for its ravages as more children are cured of diphtheria and more young persons are saved from death by tuberculosis. This explanation, however, does not seem to cover the entire ground; most physicians believe that there has been a real relative increase in the frequency of malignant growths.
A cure for cancer is urgently called for to replace the somewhat uncertain knife of the surgeon, which is curative only when applied early, and then only in about one fourth of all cases. The main trouble has been that we have not understood the true nature of cancer; we did not even know if it were infectious, let alone the infecting germ, all heralded discoveries in that direction having proved illusory. Finally, investigators bethought themselves to study animals having tumors that resemble human cancer in structure and malignancy; in this respect, mice have furnished valuable investigating material, and, even in these few years, have demonstrated certain valuable facts, especially that cancer is transplantable, but not infectious in the ordinary sense, like tuberculosis. There has also been achieved an immunization of mice against the recurrence of cancer after operation.
This brings us to the wonderful studies made by Metchnikoff and Ehrlich on the means furnished within the body for the destruction of harmful germs or the neutralization of the poisons they produce. These researches on immunity have led to interesting results: for example, we have found that the blood of one species of animal acts like a toxin to the blood of another; through this knowledge we can tell to what kind of animal a specimen of blood belongs. This has proved of incalculable advantage in a matter not strictly medical: in trials for homicide, it is now quite easy to decide whether a stain consists of human blood or of that of a lower animal. Human blood and dog blood look exactly alike under the microscope, but the laboratory test shows them to be antagonistic to each other. Several murderers have been convicted through these means.
I must mention a few more affections in which these investigations play a leading part. The best treatment of snake-bites may be said to depend entirely upon having the antitoxin at hand; snake-poison is the most typical and powerful toxin that we know. Still more curious is the modern treatment of that rare and serious affection called Graves’s disease. This complaint is due to an antitoxin in the system, produced by excessive action of the organ known as the thyroid gland. The curative serum is obtained by entirely depriving goats of that gland; these goats then become saturated with the body toxin which the gland normally neutralizes. The injection of bloodserum from these goats therefore supplies sufficient toxin to neutralize the excess of antitoxin in the blood of the patient suffering from Graves’s disease. This goat-serum treatment must be continued as long as the thyroid gland continues to be overactive, usually many months.
It may appear to the reader that toxins and antitoxins are very much alike in structure; this is indeed the case, and we label them as we do merely because the toxin is very poisonous, and the antitoxin is relatively harmless. Graves’s disease is due to an antitoxin that becomes injurious only when accumulated in the system through months and years.
V
Every intelligent person appreciates the marvelous advance in surgery, which is justly regarded as one of the greatest achievements of our time. The surgical art has indeed, until quite recently, kept well ahead of internal medicine; the tide is only now beginning to turn, partly because of the discoveries narrated in the preceding chapter, partly because surgery itself is already so near perfection. Let us, however, not forget that its phenomenal success, whether regarded from its highly developed mechanical side, or with respect to the benefits derived from physiological and bacteriological research, rests almost entirely upon the results obtained through animal experimentation.
The corner-stones of modern surgery are anæsthesia and antisepsis. Anæsthesia, by freeing the patient from the perception of pain, allows the surgeon to perform his work leisurely and thoroughly; antisepsis guards the surgeon’s efforts from eventual failure, by preventing infection of the patient’s wound.
Anæsthesia was tried on the human subject only after considerable hesitation, and after extensive preliminary experiments on animals. Morton and Jackson, the pioneers in anæsthesia, would not have dared to subject their patients to this procedure if investigations on living animals had not demonstrated its safety. The very proposal to administer a narcotic gas implies a fairly thorough knowledge of the act of respiration, and of the laws governing the diffusion of gases through the body. I have already shown how the former has been acquired; the latter has been gained similarly. To be sure, the final test of any anaesthetic will always have to be made on man himself; an operation that appears quite painless in an animal may, nevertheless, cause intense discomfort to a human being, whose nervous system is more delicately organized; furthermore, the anæsthetic may not act in exactly the same way on a man as on a dog.
As the various forms of gas-anæsthesia involve some risk in persons whose vitality is impaired, or who suffer from certain organic diseases, it was a great boon to the surgeons when Koller discovered that the eyes of animals could be rendered insensible by the instillation of cocaine. Koller was so favorably impressed by this observation that he had no hesitation in trying this drug on his own eyes, as well as on those of his patients. Our surgeons now perform a great many delicate and difficult operations with the aid of cocaine, without depriving their patients of general consciousness, or exposing them even to the slight risk of a total anæsthesia. For the methods employed in avoiding the infection of wounds, antisepsis, and its still greater successor, asepsis, we are profoundly indebted to Pasteur, who first suggested that wound-infection was caused by germs, and to Lister, who followed his suggestion and was rewarded with immediate success. Every detail of this progress has been checked off by experiments on animals.
Some of the most difficult operations concern the intestines, the great problem being to close wounds in them so tightly that they cannot leak; innumerable operations on dogs were required to determine the best method of sewing up an intestinal wound. When the question arose of linking together the two ends of a severed intestine, a simple suture was found to be imperfect; it took too much time, and was sometimes followed by intestinal obstruction. A new series of experiments on dogs became necessary, to perfect some plan of fastening the ends together with easily adjusted clasps. This was successful, and we have thus obtained that remarkable mechanical device, the Murphy button.
We are now pretty well accustomed to the idea of abdominal surgery, but operations on the brain will, no doubt, appear somewhat venturesome to the uninitiated. Indeed, were it not for the physiological study of the brain-functions, to which I have referred in a previous paragraph, we should not have advanced very far. Our knowledge of brain localization has enabled us to tell, from the patient’s symptoms, what portion of that organ is affected by a clot, tumor, or injury, and the striking of the exact spot is no longer regarded as marvelous. For example, paralysis of one limb points to trouble in a very definite area in the brain, impaired vision to another, loss of speech to a third, all as precisely mapped out as the various countries in an atlas. It is hardly necessary to repeat that we should be unable to do any of this work, had not animal experimentation shown us the way.
As to the nerves, the various resections, transplantations, and other operations, that are now accomplished by the surgeons, remind one of the activities of the telephone line-men; moreover, they are generally quite as successful. Animal experimentation has given us the clue to the various connections, and has indicated the limits to which we may go in overhauling that delicate and complicated apparatus of living batteries and wires, known as the nervous system.
Success in nerve-surgery has led to a desire to accomplish similar results with the blood-vessels. Until recently no one attempted to do more than cut diseased or injured blood-vessels out of the general circulation; even this required a vast amount of preliminary work on animals, especially with regard to the testing of ligature material, such as catgut and silk, for strength, absorbability, and capacity for being rendered absolutely sterile, the last being exceedingly difficult of determination. The effect of these operations on the local blood-supply also required investigation, for the cutting-out of a very large blood-vessel might involve the death of an entire limb. Very recent work on dogs seems to promise that the cutting-out of blood-vessels may be largely replaced by splicing and grafting; it is evident that, with the aid of such new methods, the last-mentioned risk may be avoided, and many a limb saved from gangrene and amputation. Most marvelous of all, our surgeons are now venturing to attack the heart itself; wounds of that most important of all organs have been sutured, hitherto, to be sure, with only partial success; however, we may justly expect to perfect this operation, by giving it a thorough trial on the lower animals.
This brings me to the present centre of interest in surgery, the operations on the chest and lungs. Until now, any wide opening of the chest-wall has been attended with the danger of collapse of the lungs, and instant death. It is the present aim of this branch of surgery to devise an effective method of preventing collapse of the lungs, by increasing the air-pressure within those organs. Whole series of dogs are now being subjected to procedures that aim at accomplishing this purpose, but the operation will not be tried on human beings until practice on dogs has rendered it practically perfect.
Finally, I must again insist on the fact that these operations on the lower animals are conducted under anæsthesia, in the same way as are those performed on human beings. Under the influence of ether, dogs do sometimes give forth cries, as men do under the same conditions; these noises are made quite unconsciously,as may be proved by the accounts of numberless persons who have groaned on the operating-table but did not know it until told by the surgeon afterwards. Of course, dogs suffer some pain after an operation; the same is true of us also; it is certainly no more, probably less, severe in the dog than in man. Finally, it is a rule in all laboratories, to kill maimed animals painlessly; as a proof, I shall ask my critics if they have ever seen at large an animal mutilated by surgical experimentation.