The problem of adequate and economical nutrition - admittedly a problem of primary importance to mankind in general - may perhaps be said to have developed into an experimental science at the beginning of the 17th century, when Sanctorius1 endeavored to keep himself at normal weight by having a huge pair of scales made with a chair suspended from one arm and counterpoised by the opposite scale pan. Distrusting the guidance of instinct or appetite, it was his custom to arrange a definite weight on the pan each day, seat himself in the chair and eat until the scale dipped. Although history relates little as to the progress of this experiment it is safe to conclude that the philosopher had some surprises in the course of it, and it is not strange that he did not advance very far towards a solution of the fundamental question of nutritional economy. Sanctorius died, and was forgotten or only remembered with a smile, but a later and wiser generation fell into a somewhat similar error.

Following the discovery of the relation between the quantity of heat given off when an organic food stuff was burned in a calorimeter and the energy furnished by the slow oxidation of that same food stuff in the animal organism, came the development of the calorie theory. It seemed so logical and so simple (once the mechanical difficulties had been surmounted) to calculate the amount of energy used up by a living animal in the course of twenty-four hours, and then to provide an amount of food which would furnish just that much energy, due allowance being made for unavoidable waste through lack of assimilation, for the essential protein for repair of the tissues, and for growth in the case of the young. Surely the height of efficiency was within reach. The provisioning of a family became a matter of simple arithmetic, so many ounces, so many calories. The calorie was a popular catchword, and the conscientious housekeeper weighed and measured and counted calories till her brow was furrowed with care, wondering vainly meanwhile where the energy went to when John ate 1500 calories more than the most generous accounting could possibly allow him. Battles raged round the calorie.

Should we try to "train down" to our rightful allowance or should we forget calories so far as our purses would allow us? What was the irreducible minimum in calories? How many of them must come from protein? How many might come from protein? Did it make any difference whether it was animal or vegetable protein and why? Bold spirits asserted firmly that we should follow our "God-given instincts," and pointed to many a hale and hearty bon-vivant of ripe age. Instances were multiplied of people who were saved from untold miseries by decreasing their calories, by increasing their calories, by a high protein diet, by a low protein diet. The observant advertiser took up the cry and our attention was called to the fact that for an insignificant sum we could buy sufficient calories of cereal food to maintain us for a day, a week, or a month, while the same sum expended for the more appetizing steak would hardly provide sufficient energy for an hour.

1 De medicina station apharosmi, Venioe, 1614, Translated by John Qnlncy, M. D., London, 1787.

But logical as this reasoning was, convincing as were the indisputable figures brought as proof, feeding by calories alone proved unsatisfactory. The first and most obvious cause of this lay in the qualitative differences which were shown to exist between different proteins. Proteins are composed of the units known as amino acids, but they differ in the proportions of the various amino acids present in the combination. Certain of these acids are more essential for the living animal than are the others, and if a given protein is poor in these essentials it will prove an unsatisfactory food as compared with others in which they are more abundant. In the second place, it was found that certain foods, although they contained all the necessary organic constituents and provided more than sufficient calories nevertheless failed to nourish an animal because they did not contain the inorganic salts required by the system. Careful experimentation showed how this lack could be remedied, but still the problem of nutrition was not solved.

Beginning with Lunin in 1881 various investigators endeavored to keep experimental animals alive on "synthetic diets," combinations of pure food substances put together in the proper proportions to reproduce as far as possible natural foods which were known to be adequate. One after the other reported failure. Lunin found that while adult mice could be kept alive for several months on a diet of milk alone they invariably died in less than one month if restricted to a mixture of water, milk protein, milk fat, milk sugar, and the ash of milk in which all its inorganic constituents were present, from which he concluded that there must be some indispensable substance in milk apart from the ordinarily recognised constituents. Other investigators made similar discoveries. In England Hopkins fed young rats on a mixture of purified foodstuffs and found that if the purification was carried out with sufficient care the rats failed to grow, but that the addition of an extraordinarily small amount of milk apparently provided the missing ingredient and normal growth took place.

In America, Osborne and Mendel observed that young rats fed on a diet of protein, starch, lard, and a solution containing the mineral salts of milk would grow for a short time but invariably began to fail before reaching normal size. So slight a change as the substitution of butter for lard caused resumption of normal growth and the health of the animal improved. McCollum and Davis found that the missing food substance could be obtained from the ether extract of eggs or butter, whereas lard and olive oil, although so similar in chemical nature to the latter, were valueless in this respect. Meantime Funk had been studying the disease known as beriberi. The symptoms characteristic of this disease could be produced in pigeons by feeding them on a diet of polished rice, and Funk found that birds which were at the point of death from this cause were cured with astonishing rapidity by a little of the alcoholic extract of the rice hulls. Funk assumed that the disease was due to the absence of some essential constituent which was present in the outer layer of the rice grain and was removed in the process of milling.

To this substance, the nature of which was unknown, he gave the name vitamine, a name which has been severely criticised as misleading, but which has nevertheless found a permanent place in the literature. The general resemblance betwen the substance of which a small amount prevented or cured beriberi and the substance of which a small amount seemed necessary to promote growth, led to the term vitamine being used for both, and finally this term came to signify a certain class of unidentified factors present in very small amounts in natural foods but essential for growth and well being of the animal organism.