Milk, an excellent food for infants and growing animals, contains protein (casein), fat, carbohydrate (milk sugar) and inorganic salts. The protein if given in sufficient quantity contains all the needed amino-acids. Suppose that instead of supplying our animals with milk we feed them with the isolated constituents of milk, in quantity sufficient to supply fuel needs. We give our animals an excellent protein, plenty of fat and carbohydrate to supply energy needs, and all the mineral salts necessary. From what has been said so far, such a diet should comply with all requirements.

So indeed thought most scientists until Professor Hopkins of Cambridge disproved it.*

Professor Hopkins took two sets of rats - which we shall call A and B - in about the same stage of development, and of about the same weight, and fed A with the isolated constituents similar to those that can be obtained from milk (protein, fat, sugar and mineral salts),* and B with the same substances plus a minute quantity of fresh milk.** The rats belonging to series A lost weight and showed decided pathological symptoms; those belonging to series B steadily gained in weight. On the eighteenth day the diets were reversed, so that now A was getting the little extra milk and B had theirs cut out. Almost immediately A began to gain in weight and B to lose in weight (see figure7)

* Dr. Funk calls my attention to the fact that as early as 1881 - some years before Hopkins' experiments - Dr. Lunin made the statement that "substances other than casein, fat, milk sugar and salts are indispensable" (Zeitschrift fur physiologische Chemie, volume 5, page 31, 1881).

Figure 7. - Absence of Vitamines professor hopkins' classical experiment

Lower Curve (as far as the 18th day) - Eight male rats on "synthetic" diet of protein, carbohydrate, lard and mineral salts.

Upper Curve - Eight similar rats taking, in addition, 2 cubic centimeters (two five-hundredths of a pint) of milk per day.

On the 18th day, marked by vertical dotted line, the addition of milk was changed from one set to another.

Bayliss: Principles of General Physiology.

Let us examine the results of this amazing experiment. The isolated foodstuffs yielded energy in quantity more than necessary to satisfy all calorific requirements. The protein was rich in the necessary amino-acids. The mineral salts were not only abundant but various in kind. The fat and carbohydrate were there too. Yet all this was of no avail. The animals lost weight almost as rapidly as if they had been starved. When, however, a minute quantity of fresh milk was added - about two five-hundredths of a pint per day - the animals thrived.

The amount of milk added was so small that it could not have added anything material to the energy value of the food. Besides, the energy value of the foodstuffs was more than sufficient. And in so far as the most careful chemical analysis could show, the whole milk added was itself composed of nothing but protein, fat, carbohydrate and mineral salts, with the rest of it very little more than plain water. In other words, the chemical composition of the whole milk did not materially differ from the chemical composition of the constituents isolated from milk. Was the difference due to something in the milk other than fat, protein, carbohydrate and mineral salts? If so, this "something" must be present in exceedingly small quantities, since the addition of two five-hundredths of a pint of whole milk was sufficient to exhibit such striking effects.

* The fat used was not milk fat but lard. This, as will be brought out presently, is most important.

** Plenty of water is always included in such studies.

Startling as this experiment seems, the result was not altogether unexpected by the scientist. He had already acquainted himself with a number of substances, present in minute quantities in the body, the absence of which caused profound disturbances to the system. Thus adrenalin, or as it is sometimes called epinephrin, is present in the blood to the extent of one part in one hundred million; yet it is said to be essential to life. The very ferments or enzymes that simplify our food in the digestive tract so as to prepare it for absorption, are present in exceedingly minute quantities; yet they are essential. If, then, there is some substance in food, present in microscopic amounts, without which life cannot continue, it was an interesting, though not wholly an unexpected discovery.

Vitamine

At this point we shall anticipate a little and state that the name vitamine has been given to the substance or substances - such as the

"something" in milk - which, though present in minute quantities in foods, are absolutely essential to a continuation of the life process.

The word vitamine was coined by Casimir Funk, a Pole. The first part of the word indicates its relation to the life process; the second, to its chemical nature. As we shall see, objections have not been wanting to the use of the word.