144 HUMAN PHYSIOLOGY 



Proteids which are soluble and can be assimilated are, 

 without doubt, also digested, but the extent of this digestion 

 cannot be stated. The digestion of proteids capable of 

 assimilation is, however, of real significance, since their rate 

 of absorption is thus increased. 



Absorbed proteids reach the blood, most likely, chiefly in 

 the form of albumin, as the quantity of serum albumin of the 

 blood is increased by the eating of proteids. 



Concerning the further history of proteids in assimilation 

 nothing is known. 



3. ABSORPTION AND ASSIMILATION OF FATS 



From the fatty acids or soaps and glycerin formed by the 

 splitting up of fats during digestion, neutral fats are again 

 formed in the mucosa of the intestines. Even if fatty acids 

 or soaps are eaten, neutral fat is present in the lymph; in 

 this case the glycerin necessary for the formation of neutral 

 fats must have been formed in the intestinal wall itself. If 

 a mixture of soap and glycerin is heated with the intestinal 

 mucous membrane, neutral fats are also formed. This forma- 

 tion of neutral fats takes place in the epithelial cells. During 

 the digestion of fats the epithelial cells of the intestine are 

 filled with fat droplets of various sizes. 



But the fat found in the epithelial cells is not necessarily 

 derived from the union of the fatty acid and glycerin taking 

 place in these cells; for neutral fats in the emulsified state 

 may be taken up by them directly. 



The opinion is current that most of the fat is absorbed in 

 the emulsified condition', and that only such a quantity of fat 

 is split up as is necessary to furnish the fatty acids or soap 

 needed for this emulsification. But the correctness of this 

 view is doubtful because the other necessary condition for 

 emulsification the alkaline reaction of the contents of the 

 intestine is frequently wanting. The contents of most of 

 the upper part of the small intestine have an acid reaction 

 due to free fatty acids; yet here fats are also absorbed, as is 



