544 MECHANISM OF ABSORPTION. [BOOK n. 



symptoms, such as convulsions and the like. This suggests that 

 under normal circumstances proteid food passing into the portal 

 system undergoes in the liver changes which fit it for being 

 thrown upon the general circulation ; when it does not pass 

 through the liver and therefore does not undergo these changes it 

 acts as a poison. The further inference is of course that proteid 

 food is absorbed by the portal vein and not by the lacteals. 



We may therefore say that the results of experiment while 

 they do not definitely prove, give some support to, and at 

 least do not contradict, the view which we a little while ago put 

 forward as probable, namely, that the proteids 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 

 performed 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 



