any piece of prolonged, hard work, mental or physical. As soon as we realize that to be strong and healthy is not the same thing as to increase the size of our muscles, the individual element in exercise becomes more and more prominent. If one could prescribe gymnasium exercise to increase muscle and thereby health, the individual element could be largely disregarded, but when one recognizes that the muscular individual is not necessarily healthy, the individual element in the choice of exercise comes to the fore. Some persons enjoy pulling chest weights, and are benefitted by it (perhaps because they enjoy it), but the vast majority of people would rather be put to penal servitude than pull chest weights, and in such persons it certainly may do harm. We need to take that crude product which we call "exercise" and smelt out of it what is of value. We believe that the more fully it is analyzed the more the individual factor will be recognized. Is it deep breathing, vigorous heart action, profuse perspiration, that is that valuable element? Is it relaxation, enjoyment, change of mental attitude? Is it the amount of fresh air breathed in? One thing we believe is demonstrably true in most persons, viz., that in valuable exercise there is no self reference. Attention is turned away from self. In exercise which you enjoy that is the case. But many exercises prescribed, as for example the Swedish system or any other system of gymnastics, calisthenics, etc., which is done for exercise and not for fun, direct the person's attention to himself and thus in a large proportion of cases neutralize any possible good to be accomplished through them.

6. Food.

First, in regard to the amount. The vast majority of us have the idea that when the patient is run down we should feed him up. But the recent investigations of Prof. Chittenden should certainly make us more doubtful of the value of feeding persons up. Prof. Chittenden has shown that Voit's diet-tables can no longer be regarded as a standard for all persons. Some persons on a diet containing a very much smaller amount of proteid and possessing a lower calory value do not only as well but apparently much better. We are not arguing that the diet used in Prof. Chittenden's experiments is right for all of us, but merely that he has directed attention to important individual differences. Apparently certain persons are better off on what is practically a vegetarian diet. Let those who find it to be good for them, adopt it, though they need not mount to the housetop and proclaim that every one must follow that diet or be damned. The brilliant work of the Russian physiologist, Pawlow, emphasizes in another way the same point; he shows that the dog's gastric juice will not flow if the animal has no taste for the material offered it.

In regard to the use of water, many rules seem to be constructed in the following way. A person comes to us, in ill health; we find that he drinks very little water. We prescribe water; he gets better, and we then formulate the rule that the ordinary man should drink more water. But if we should investigate not the hygienic failures who come to doctors' offices, but the people who are strongest, and healthiest, we

should probably find that many of them drink very little water or liquid of any kind, very much less than we, as physicians, are in the habit of saying that people must drink to be well. We believe that this is an individual matter and that no invariable rule can be laid down.

7. Tests of Health.

We are very much in need of tests of the degree of health, tests that will show a supposedly "healthy" person, whether he is below par and if so how much. In such cases individual differences are likely to count a great deal. Some persons are to be considered well if they eat well and sleep well and feel well. For others these tests are not sufficient. We have noticed in quite a number of persons that information of some value can be obtained by noting the degree of infection of their hang-nails. Everybody has some hang-nails, but when the individual is below par, they begin to get inflamed. Another possible test is the condition of the reflexes, some of the minor reflexes, especially. In the last report of Phipps Institute for Tuberculosis there is an account of the reflexes of tuberculous patients, especially the hypothenar reflexes. One of us has watched in himself for some time the condition of this reflex as compared with his own general condition, and we are beginning to watch it in some other persons as well. One of us finds that when he loses sleep or is overworked, this hypothenar reflex comes out very prominently (scratching the ulnar side of the forearm with a pencil makes the abductor minimi digiti stand out). When he is in a first rate condition it cannot be brought out. Perhaps certain individuals can measure their condition by noting the condition of their reflexes.

We have endeavored to remind you of a large body of facts which indeed are common knowledge or common ignorance, but which are not always in that foreground of our minds whence action issues. These facts exemplify the individual variations dependent:

(a) On our chosen plan of life.

(b) On our environment, age, sex and occupation.

(c) On our inherited or acquired temperament, taste and bent. (d) On the selective bent of our individual tissues, which make a certain amount and kind of rest, exercise, food, sleep, suit us as they do no one else.

III.

Now are these differences of individuality such as to preclude the possibility of framing any set of requirements for health, such as our hygienic books have usually contained? A "required course" for health, we answer, like required courses in college, will soon become extinct, but a group-elective system will remain. From among a group of possible ways of being well each man will have to choose one by instinct and experiment. For example you belong either to the group of those who can rest by change of work or to those who cannot; instinct and experiment will enable you to judge. You are either a no-breakfast man or you are not, and so on.

To work out the actually existing and practicable methods of keeping well, at or near which each man is likely to live is the job to which

we propose to devote a good deal of time and money during the coming years. We propose to collect, if we can, the statistics of the actual habits of 50,000 healthy Americans, the healthiest that we can get in touch with through physicians and other intelligent persons in different parts of this country.

How has hygienic success been actually achieved? What methods of keeping well are the most often successful in this country at the present time?

Imagine, for example, that statistics should show that 80% of healthy Americans eat 3 meals a day, 5% eat no breakfast, and 4.5% no lunch, while only 2% skip the evening meal. It would hardly be worth while to experiment much with a no-dinner plan, but one might want to find out by experiment whether one is better without breakfast or without lunch. If it should turn out to be true that 1⁄2 the healthiest people to be found eat meat but once a day, while a third eat it twice and the balance three times a day, one would wish to try these experiments, but would not consider it worth while to try eating no proteid whatever, nor making one's diet exclusively proteid.

In colonial days when our race was more homogeneous and the range of our possible activities more limited than they are now, the variety of hygienically successful methods of living may very well have been fewer. Just as all gentlemen were in colonial times of one religion and belonged to but 2 or 3 professions so it may very well have seemed as heretical to speculate or experiment in hygiene as it was in religion. Authority decided such matters.

Now with the freedom of conscience and the right of private judgments in politics and religion, are coming, we believe, the right and the duty of the individual layman to prevent disease in himself by working out for himself his own method of keeping well.

Anyone who has watched himself carefully must have noticed how sharp and clean-cut his individual limits are. You can walk easily for miles just inside your individual limit of strength, but if anyone pushes you even a little way beyond it, you are tired in 15 minutes. It will tire you almost as much to have to hold your pace down to that of a slow walker as it would to hurry after the champion pedestrian. By instinct and experiment you find your proper pace and then it varies little for years. So it is with sleep, food, recreation. You can work for months. just within your normal sleep limits, but if you cut down sleep even 1⁄2 hour a night below your limit it will show at once in the quality of your work, if not in more obvious forms of ill-health.

The individual's best path of life, then, is sharply marked out and not difficult for him to determine. But it may be almost impossible for any outsider to determine it even if the outsider is a physician. Suppose someone else tried to decide for you how fast you should walk, what the natural swing of your gait should be. He might by very careful and constant observation of your various paces come fairly near the right one, but it would be a great waste of energy for a result only approximately correct.

The individual should be urged to find for himself how to keep well. We count it a great misfortune or disgrace if an American arrives at manhood without knowing the 3 R's., but we think it needs only a little reflection to make us realize that it is a far worse calamity to grow up without knowing what rests you, whether change of work is your best recreation, whether you are better with a low proteid diet, a low or a high intake of water, and what your avocation (or hobby) is.

Have you not sweated blood in the attempt to discover for a man of 40 what his proper avocation is, or for a woman of 35 what is her proper work? And as you labored has it never aggravated your toil to recognize that this job should have been done by the patient himself years before?

To find out for another man how he ought to live is as awkward as to tie his necktie for him. You can do it somehow or other but he can feel his way and adjust his motions much more accurately himself.

The individual factors in hygiene are so many and so essential that in the great movements of preventive medicine it is the layman who with some general guidance must work out the salvation that will make. for the best hygiene in the future.

We are aften told that doctors should prevent disease instead of trying to patch up the poor wrecks who exemplify the sad results of long years of hygienic failure. But we do not believe that the most important work in this line can be done by the doctor. It is a waste of energy for him to attempt it in most cases, and moreover, the educated layman will more and more resent the attempt.

We believe it will not be long before it will be held as presumptuous for us to attempt to prescribe a man's best way of living by general rules, as it would be for us to prescribe his political or religious opinions. Private judgement and unwillingness to submit to authority will spread to this sphere, nay have spread far in that direction already.

We wish to recur for a moment before finishing to our own plans. Our belief is (as we have tried to indicate) that the hygiene of the future will be not a series of commands "thus do or thou shalt die," but a map showing a number of practical roads, each preferred and found. satisfactory by a group of persons of a certain build, a certain ideal of life, a certain inherited and acquired "set" in their tissues. "On or near some of these roads," we shall say, "you will probably travel. Look them over as you do in choosing a profession, a house or a town to settle in. Find out which suits you best and follow it."

Now our ambition is to assist in the construction of this map, to find out by the collection of a large body of statistics of healthy people what workable sets of habits now exist in regard to food, water, exercise, sleep, work, recreation and the rest. Such a map of passable roads will not bind the individual to walk on any one of them but if he wishes to roam in the fields or ditches he will at least be conscious of what he is doing and where the ordinary roads are in case he cares to return.

To collect a body of statistics on which such a map can be based will need the co-operation of many intelligent persons all over this coun

try, and later we shall be asking many of you gentlemen to co-operate with us in the task.

THE CHEMISTRY OF DIGESTION.*

By CHARLES D. AARON, M. D.,
Detroit, Mich.

The first definite knowledge we have of the chemistry of digestion is the work of William Beaumont (1), a surgeon in the United States army who made his observations on a young Canadian, Alexis St. Martin, who from an accident, had a fistulous opening in the stomach through which Beaumont was able to watch the process of digestion and remove the gastric juice for analysis.

Until the establishment of the theory of chemical solution by Spallanzani, it was supposed that digestion was some sort of putrefaction, trituration or maceration. Spallanzani taught the solvent action of the fluid secreted by the stomach. It was he who gave the name gastric juice to this fluid. Beaumont proved that the secretion of the stomach was able to dissolve certain foods and he showed that the gastric juice contained free acid. He collected the gastric juice and repeatedly examined it and to confirm what he found he sent a sample of this liquid to Professor Dunglison, professor of chemistry in the University of Virginia, and to others for analysis. Professor Dunglison reported that the sample examined contained free muriatic acid and acetic acid, phosphates and muriates, with bases of potassa, soda, magnesia, lime and an animal matter, soluble in cold water, but insoluble in hot water.

The proof of the existence of pure hydrochloric acid in the juice of the stomach we owe to Beaumont. Very little of the chemistry of digestion was accomplished after 1834, when Beaumont wrote his book on the "Experiments and Observations on the Gastric Juice and Physiology of Digestion," until 1867 (2), when the stomach tube came into use.

In 1875, Ewald (3) introduced the soft rubber stomach tube, which enabled us to remove the stomach contents with ease. From this time the chemistry of digestion made rapid progress, as many investigators began to work on its development. It was not until 1885 that the experiments of Beaumont were really confirmed and we could say absolutely that there was a free acid in the gastric juice. We are now able to demonstrate accurately, up to certain limitations, the chemistry of digestion.

We owe much to Pawlow (4), of St. Petersburg, who has recently done a great deal of experimental work on the chemistry of digestion. The reaction of the saliva is alkaline and ptyalin is active in an alkaline or neutral medium. Free hydrochloric acid in the stomach inhibits the amylolytic action of the saliva. Chittenden Smith concludes on the action of acid on the amylolytic power of saliva as follows: "The most favorenzymes and are converted into active ferments by hydrochloric acid. Hydrochloric acid will convert inert pepsinogen and renninzymogen into active ferments, pepsin and rennin, in less than one minute. Lactic acid *Read before the Detroit Academy of Medicine, January 24, 1905.