If carbohydrates supply energy, and proteins, material for tissue repair, what does the vitamine supply? We really cannot answer this question very satisfactorily. Some liken vitamines to enzymes as being in the nature of catalysts. By a catalyst we mean a substance which influences chemical reactions without itself undergoing any ultimate change.

* Dr. Williams has devised a very delicate test for this vitamine. It depends upon the fact that yeast cells cannot grow and multiply unless water-soluble B is present. The procedure is to take single yeast cells and mix them with drops of different solutions that are under examination. If the solution contains water-soluble B the yeast cell will grow; and indeed the extent of growth gives us an idea of the amount of vitamine in solution. All this can be examined under the microscope. Where the water-soluble B is absent, no growth occurs. Dr. Williams' work, however, needs further confirmation.

Others are of the opinion that they are of the nature of hormones, - the active substances present in the various internal secretions (such as those in the thyroid and the adrenals) - in that they probably stimulate activity in the cells. Still others consider that their function is to supply certain chemical groups to the body which are quite essential, and which the body itself cannot manufacture.

In connection with these speculations, Dr. Steen-bock has made the interesting observation that one of these vitamines - fat-soluble A - is always associated with a yellow pigment. Butter, egg yolk and codliver oil are all highly colored with this pigment. Colored roots such as carrots and sweet potatoes contain it, but sugar beets and Irish potatoes have little or none. These observations lead Dr. Steenbock to conclude that the yellow pigment and the fat-soluble A are very closely related. This view, however, has met with very much opposition.