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 in adults, 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 serum 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 VOL. 106-NO. 1

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.

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. Anæs

thesia, 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 anæsthetic 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 anaesthetic 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 neces

sary 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

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

sia, 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.

In a paper in the Atlantic for June, I discussed at some length the development in America of the ideal training of the physician. In the present article it is my purpose to deal with the actual conditions in the medical profession of the country, with especial reference to the number of doctors we are now endeavoring to support. The problem involved in reaching a satisfactory physical adjustment is practical, not academic; and taking economic and social conditions as they are, its solution will depend upon the widest possible distribution of the best possible type of physician. For an intelligent consideration of the question, it is fun

damental that we understand the statistical aspects of medical education in America so far as they are immediately pertinent to the question of reform.

Professor Paulsen, describing in his book on the German Universities the increased importance of the medical profession, reports with some astonishment that 'the number of physicians has increased with great rapidity, so that now there is, in Germany, one doctor for every 2000 souls, and in the large cities one for every 1000.' What would the amazed philosopher have said had he known that in the entire United States there is already on the average one doctor for every 568 souls,