INTERNAL RESTITUTIVE SECRETIONS 



273 



dogs, where, on the other hand, there is more adenoid tissue (see 

 Fig. 89). It is difficult to reconcile this fact with the theory 

 that the central lacteal serves exclusively for absorption of fatty 

 substances. 



I. Munk, who upholds this doctrine, himself cites in his Text- 

 look, in addition to the data he obtained from man, the results of 

 the comparative analyses of lymph and chyle made by C. Schmidt 

 and Fr. Simon and Rees on various animals, which appear to us to 

 speak in favour of a less exclusive theory. To facilitate com- 

 parison we have arranged these data in one table : 



IV. The history of physiology has not seldom shown that new 

 achievements in the field of physical science give rise to the 

 illusion that a part of the mystery which veils the subtle mechanism 

 of the vital processes has been cleared away. After Dutrochet's 

 discovery of diffusion through permeable membranes of substances 

 in solution, it was held by many, without direct experimental 

 tests, that Food Absorption in the Intestine was a phenomenon of 

 the same order, easily explicable on the laws of osmosis, and that 

 the sole physiological object of the chemical processes of digestion 

 was to render the ingested foods diffusible through the animal 

 membrane formed by the epithelial layer of the intestine. 



But when this doctrine came to be experimentally tested a 

 number of facts were brought to light which showed that intestinal 

 absorption is no such simple phenomenon, and that the living 

 walls of the intestine are not comparable with an inert porous 

 membrane. 



As early as 1869, Voit and Bauer observed the absorption of 

 blood serum injected into a loop of intestine, a phenomenon that 

 cannot be explained by a simple process of diffusion : few, however, 

 realised the importance of this fact, and the absorption of fluids 

 from the intestine continued to be regarded as an effect of osmosis. 

 Hoppe-Seyler (1881) criticised this theory, and held that the 

 passage of the intestinal fluids into the circulation was not a 

 simple effect of the chemical differences between fluids separated 



VOL. II T 



