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 pro

tects 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. phoid 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 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

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.

per

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 sons 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