I propose to give a few lectures on the subject of diet. Diet plays so important a part in health and disease that every physician should be well informed on all points pertaining to it. It should really form the basis of every medical study. It is the A, B, C of medicine. We cannot live without food and we cannot treat anyone without a certain dietary; and if we understand all the relations of diet a great deal can be accomplished by it alone in the treatment of disease, without the aid of medicine. Diet comprises all the questions relating to food, and food forms the basis of all animal life. Food contains all the substances found in the living organism, because the body develops upon it; it grows up from the little baby to the big organism. Nothing is added to the body excepting what is derived from the food.

1 Lectures I, II, III and IV on Dietetics have been delivered at the Postgraduate Medical School and Hospital and have appeared in the Postgraduate Journal of July, August, September and October, 1913.

On the other hand, food contains only the substances found in the earth. Everything that we eat, animal or vegetable, originated in the soil under one form or another. That means that whatever we have in our bodies comes from the earth. The Bible says: "From earth you are made and to earth you go." Nowadays we speak of the different elements found in the body. We have analyzed the latter and know that there exist the most varied substances: carbon, nitrogen, hydrogen, oxygen, calcium, magnesium, iron, phosphates, sulphur, etc.; but in the end the old philosophers were right. If we should take earth, even if we have all the elements, carbon, calcium, phosphate, etc., we could not accomplish anything with it, but after these substances have been changed by living matter and developed in the forms in which they exist in either animals or plants then it is fit for our organism. It has first to undergo this radical change through living matter.

Thus far we have not been able to accomplish these changes artificially; that is, we cannot put inorganic matter together so as to bring it into life. We require another living medium to accomplish this change. Every living cell must originate from another one. So living plants develop from the seed into plants. There must first be something that is alive to bring forth new life. We know nothing yet of how inorganic matter develops into an organic being. It may be that the great chemists and physiologists think it originated of itself, but we do not know about that for the present. So far as we can tell, nothing is developed of itself, but every animate being is developed from some living individual. Our food, then, consists of either animal or vegetable matter. We find some nations living principally on animal diet, and some animals living on animal food exclusively; others live on vegetable material alone, and some nations live principally on vegetable food. That shows that either of the two is feasible, - that persons can live either on vegetable food alone or on animal food alone. If one should ask which is the better way, it is generally admitted that a mixed diet is the best for mankind. It has been shown that those nations which subsist on a mixed diet, taking both animal and vegetable foods, have accomplished most in the way of progress. Those nations which live exclusively on animal diet, such as the Esquimaux, or the peoples to the far south where vegetable material is rare and who live almost exclusively on the fish and animals which they hunt and kill have not accomplished very much in the way of progress. On the other hand, the peoples of India, China, and Africa live mostly on a vegetable diet, and these nations have not accomplished very much either, in the way of progress. It is possible to live in either way, but as a whole, physiologists have decided that a mixed diet, combining the two forms of food material, is the best to develop the mental faculties to the highest degree.

It has always been known that you cannot live without food; if you do not take in food, the body loses weight, and finally dies; but until recent years not much has been known of the exact amount of food required by nature to maintain life and to keep the body in good condition. The amount is almost mathematically prescribed, and in recent years this amount has been determined. This has been learned as follows: First, it has been determined in a general way how much food grown persons require. It is noted how much one person, a second, and a third eat for breakfast, dinner, and supper. This is carefully written down, and then the average amount consumed is calculated, and so we know about what amount of food is required by normal persons in health. That gives a fair indication of how much is needed.

Now, before going to the amounts required, I will say a few words about the different classes of food. While every diet must contain all the elements necessary for life, the food has been divided into three large classes, because they all contain more or less of the elements necessary for life. These three groups are the proteins, carbohydrates, and the fats. Among these are also found the so called "vitamines," contained in milk, eggs, cereal, green vegetables, and fruits.