516 MECHANISM OF ABSORPTION. [BOOK 11. 



diffusible peptones, pass into the blood vessels and not into the 

 lacteals. 



But, if this view be provisionally accepted, it must be on the 

 understanding that it is probable only ; and it may be that 

 proteids do not take the same paths and are not absorbed in the 

 same condition in all animals. The experiments just related were 



Serformed on dogs, that is to say on carnivorous animals whose 

 natural) food contains a considerable quantity of fat, and whose 

 lacteals might therefore be considered as preoccupied in the 

 absorption of fat. The food of herbivora on the other hand 

 contains a relatively small amount of fat ; and if in these animals 

 all the proteids and carbohydrates are absorbed by the blood 

 vessels, there is comparatively little left for the lacteals to do. 

 Yet in these animals the lacteals and the lymphatics are well 

 developed. In the villus of a herbivorous guinea-pig or rabbit, 

 though the reticular tissue is very scanty as compared with that 

 present in the villus of a dog, the lacteal chamber is, relatively 

 to the diameter of the villus, not merely as large as but much 

 larger than in the dog. It is difficult to suppose that this wide 

 chamber is intended solely for the absorption of the relatively 

 small amount of fat present in vegetable food. The question 

 which we are discussing is clearly at present to be regarded as 

 by no means settled. 



The Mechanism of Absorption. 



310. The Absorption of Fats. We have now to consider 

 the manner in which these several substances pass into either the 

 lacteal radicle or the capillary blood vessel. It will be con- 

 venient to begin with the absorption of the fats. 



We have seen reason 280 to think that the fats, remaining 

 chiefly as neutral fats, are emulsified in the intestine, by means of 

 the bile and pancreatic juice, the small quantity of soap which is 

 formed probably serving simply the purpose of facilitating the 

 emulsification. 



The neutral fats so emulsified pass in the first instance into 

 the bodies of the columnar cells of the villi. It has, it is true, 

 been maintained by some that they pass between the cells and 

 not into them ; but the evidence is distinctly against this view. 

 The cells may again and again be seen crowded with fat, and 

 the cases in which the fat has been seen between the cells and 

 not in them are due to the extrusion of the fat, during the shrink- 

 ing of the villus in the course of preparation, from the cells into 

 spaces between the cells. In the frog, in which there are no villi, 

 and in which the folds of mucous membrane serving the purposes of 

 villi do not so readily shrink, the presence of fat globules in the 

 cells after a fatty meal can always be easily demonstrated by 

 osmic acid preparations. Since no such collections of fat globules 



