Digestion being completed, and the available portion of the foodstuffs thereby converted into forms suitable for absorption, the question naturally arises, In what manner are these products transported from the alimentary tract to the tissues and organs of the body? In attempting to answer this question, we shall find many illustrations of the precise and undeviating methods which prevail in the processes of nutrition. For example, it would seem plausible to assume that the different forms of sugar entering into man’s ordinary diet, all of them being soluble, would be directly absorbed and at once utilized, but such is far from being the case. Milk-sugar and cane-sugar, both appearing in greater or less degree in our daily dietaries, if introduced directly into the blood, are at once excreted through the kidneys unchanged. The body cannot use them, and they are gotten rid of as speedily as possible, much as if they were poisons. When taken by way of the mouth, however, they are utilized, simply because in the intestine two enzymes are present there, known as lactase and invertase, which break each of the sugars apart into two smaller molecules. In other words, milk-sugar and cane-sugar are disaccharides, and if they are to be absorbed in forms capable of being made use of by the body they must be split apart into simpler sugars, viz., monosaccharides, such as dextrose, levulose, etc. The great bulk of the carbohydrate food consumed by man is in the form of starch, and this, as we have seen, is converted into maltose by the action of saliva and pancreatic juice. Maltose, however, like cane-sugar, is a disaccharide, and the body has no power to burn it or utilize it directly; but in the intestine and elsewhere is an enzyme termed maltase, which breaks up maltose into two molecules of the monosaccharide dextrose, and this the body can use. Man frequently consumes starch to the extent of a pound a day, and if utilized it must all undergo transformation into maltose, and then into dextrose. There is no apparent reason why maltose should not be absorbed and assimilated as readily as dextrose, but so urgent is the necessity for this conversion into dextrose that in the blood itself there is present maltase, to effect the transformation of any maltose that may gain entrance there. We are here face to face with a simple fact in nutrition. The body cannot utilize disaccharides directly. Why it is so we cannot say, but the fact is a good illustration of the principle that nothing can be taken for granted in our study of nutrition.