278 PHYSIOLOGY CHAP. 



case for fats and proteins. Of this there can be no doubt, either for 

 salts or sugars. We saw in the last chapter that all the alimentary 

 carbohydrates are converted by the chemical processes of digestion 

 into monosaccharides, i.e. into the form of simple sugars, more 

 particularly into glucose, before absorption. They are thus 

 absorbed and carried to the liver by the portal system in that form 

 in which they circulate normally in the blood. The disaccharides, 

 i.e. saccharose, maltose, and lactose (which are bimolecular 

 anhydrides of the monosaccharides) are not usually absorbed as 

 such, but are first hydrolysed, with addition of one molecule of 

 water, by the action of the succus entericus. It is only when 

 highly concentrated solutions are introduced that they are partially 

 absorbed unchanged, the proof of this being that when they reach 

 the blood they do not remain there, but are at once excreted by 

 the kidneys. The polysaccharides, i.e. dextrin, the starches and 

 gums, and cellulose (which are polymeric anhydrides of the simple 

 sugars) cannot be absorbed without first undergoing the amylolytic 

 action of the saliva and pancreatic juice. Dextrin and amygdalin 

 alone are sometimes held to be absorbed in small amounts, but 

 this fact has not been proved, and is in any case very obscure. 



V. The question of the process of Fat Absorption, and the 

 chemical form into which the fats must be converted previous to 

 absorption, is more complicated. 



Till recently, the theory that fat was principally absorbed in 

 the form of a fine emulsion of glycerides (or neutral fats), a fraction 

 only being absorbed as soaps (formed by the combination of the 

 fatty acids liberated by the lipolytic action of steapsin and the 

 intestinal bacteria with the alkali of the secretions of the 

 intestine) was uncontested. On this theory the cleavage of the 

 glycerides is not a digestion, indispensable to the absorption of 

 the fat : it merely furnishes a small amount of soluble soaps 

 which facilitate the emulsification of the neutral fats these 

 being mainly absorbed as an emulsion of microscopic granules. 



This theory was first put forward by Briicke, and was after- 

 wards supported by the physiological and histological observations 

 of several authors. But further advances in research cast grave 

 doubts upon its probability at least as a general statement. 



In order to remove the difficulties encountered in regard to 

 the mechanism by which the fat globules could penetrate into the 

 interior of the epithelial cells, Perewoznikoff (1876) and Will 

 (1879) proposed the hypothesis that the whole of the ingested 

 fats are split into fatty acids ; that they are absorbed in this form 

 or as soluble soaps by the epithelium ; and that when absorption 

 has taken place, they are regenerated into glycerides or neutral 

 fats by a synthesis performed by the anabolic activity of the 

 epithelial cells. These authors demonstrated that in the frog, after 

 feeding with pure fatty acids or soaps, with or without the addition 



