624 SPECIAL PHYSIOLOGY. 



stomach, is chiefly performed by means of the bloodvessels, because 

 the gastric mucous membrane is destitute of villi, and, therefore, of 

 proper lacteal vessels ; nevertheless, nutrient and other substances, 

 prevented from entering the intestine, by ligature of the pylorus, have 

 been shown to be absorbed by the gastric lymphatics. The process 

 by which certain parts of the food are absorbed by the bloodvessels of 

 the alimentary canal, must be identical with that of the general absorp- 

 tion of soluble substances from other vascular surfaces, or tissues, of 

 the body. Like the latter, it partakes of the nature of the physical 

 processes of liquid diffusion and dialysis. Water, and substances dis- 

 solved in it, such as soluble salts, sugar, extractive matters, and solu- 

 ble albumen or albuminose, permeate the epithelial and subjacent layers 

 of the mucous membrane, and also the thin coats of the capillaries and 

 smallest venules, not merely of the villi, but of the general surface of 

 the intestinal canal, in the same manner, probably, as a similar solution 

 would pass through moist dead animal membranes. The temperature 

 of the interior of the body greatly favors the osmotic process. The 

 penetration of the water with its dissolved contents, is a dialytic phe- 

 nomenon ; and by a similar action, the entrance of certain substances 

 is probably permitted more readily than that of others, the crystalloid 

 substances, such as the salts and sugar, with the creatin and creatinin 

 of the extractive matters, and also the albuminose and gelatin peptones, 

 entering more readily than the colloid substances, such as dissolved 

 starch, mucilage, albumen, gelatin, and the non-crystallizable ex- 

 tractive matters. But dissolved colloidal starch is converted by the 

 saliviri into the crystalloid sugar ; and albumen and gelatin, when di- 

 gested by the acid pepsin, are changed into albuminose and gelatin 

 peptones, which, though not true crystalloids, are much more dialyzable 

 than the albuminoid and gelatinoid substances contained in our food. 

 The molecular metastases, or changes in question, may be in some way 

 connected with a -process of Jiydration. It has also been suggested that 

 a colloid body may be formed by groups of crystalloids, and so its tem- 

 porary metastasis from one condition to another may be explained. 

 It is possible also that there may be special reactions between alimen- 

 tary substances and the living mucous membrane and walls of the ves- 

 sels, favoring or resisting the passage of some or other of those sub- 

 stances. But this is uncertain; and the act of absorption by the 

 bloodvessels is so easy, rapid, and general, in the case of non-nutrient, 

 and even of many poisonous substances, that their walls can possess 

 but little if any power of selection or exclusion. Fatty matters, how- 

 ever, unless in a state of saponification, do not readily, or at all enter 

 the bloodvessels. Experiment has shown that even when finely divided, 

 as they exist, for example, in the yolk of the egg, and in milk, they 

 may be made, under moderate pressure, to permeate moist membranes 

 (Heidenhain) : and further, that the natural repugnance between oil 

 and wetted membranes, is much overcome, if these latter are saturated 

 in alkaline solutions or in bile. (Wistinghausen.) A temperature of 

 100, or that of the interior of the body, facilitates this permeation of 

 fat. Though acids generally, and especially the hydrochloric acid, 

 which exists in gastric juice, are rapid dialyzers, and so penetrate very 



