It is possible to determine what quantities of each type of food substance, of water and of salts are required in the daily diet of an organism. Naturally a ’balanced ’diet, I.e. one supplying these substances in the right proportions, has been most accurately worked out in the case of the human organism since we know more about the human body and its working than that of any other animal. The mammalstheir young on milk, which must therefore be a perfect food since the great majority of them grow up into normal healthy individuals. Cow ’s milk contains 3-2 per cent. of proteins, 4-0 per cent, of lipides, 5-0 per cent, of carbohydrates and 0-7 per cent, of salts, the remaining 87-1 per cent, being water. Such a food as milk is admirably suited to a young animal, but would be far too dilute for the nourishment of the adult. A grown man would have to drink nearly 1 gals, per day. Sir Gowland Hopkins, a biochemist, in 1912 showed that when young rats were fed on artificial milk, I.e. milk made by mixing its constituents, artificially made but in the right proportions, they thrived for a time, but later became unhealthy, lost weight and one set eventually died. Upon adding a very small quantity of natural milk to the artificial milk, another set thrived and grew up into normal animals, indicating that the natural milk supplied some potent substance essential for normal development and health. A number of these substances, called vitamins, are now definitely known, the chief being denoted by the letters A to E. In the days when long voyages were first undertaken the crew were liable to suffer from the disease scurvy, which we now know to be due to the fact that their food, which had of necessity to be dried or pickled, lacked vitamin C. Bcri-beri is a disease which has long been known amongst the rice-eating peoples of the East. Eijkman, a Dutch physician, in 1897 noticed that domestic fowls fed on ’polished ’rice suffered from a disease strangely resembling beri-beri, whereas those fed on untreated grain were healthy. We now know that beri-beri is due to lack of vitamin Ttlt which is present in the outer layers of the rice grain.
Although we do not yet know what some of these vitamins are, nor how they act, it is clear that they are extremely potent, a few milligrams of each being sufficient per day in the diet. This seems to show that their action may be catalytic, although they do not seem to be like ordinary enzymes.
The ’vitamin diet, ’ would be complete if it included fresh milk and butter, wholemeal bread or yeast extract, and orange juice. Further, since many vitamins are destroyed in various cooking processes, some fresh uncooked food is highly desirable.