202 MANUAL OF PHYSIOLOGY. 



possible it would not preclude the possibility of their passing 

 through the intestinal wall, which presents no such obstacle, for it 

 is a living structure that can overcome such physical difficulties 

 as the non-diffusion of colloids. When we know that solid par- 

 ticles of fat can enter the lacteals we can have no difficulty in be- 

 lieving that a solution of albumin is admitted. We may then 

 conclude that it is not only possible, but even probable, that a 

 good deal of proteid is absorbed as ordinary soluble albumin. A 

 certain limit to proteid absorption exists, so that any albuminous 

 materials above the maximum that escape conversion into leucin 

 and tyrosin are thrown off with the faeces. 



In the absorption of water, watery solutions of salts, sugars, 

 and peptones, there are no physical difficulties to be got over ; 

 so that we are in the habit of speaking confidently about the 

 mechanism of their absorption, although in all probability many 

 circumstances of which we are ignorant co-operate in bringing 

 about the results which seem to us so simple. 



It is not the same, however, with the fatty food-stuffs. A small 

 quantity of these may no doubt be split up into soluble glycerin 

 and fatty acids, which are at once changed into soluble soaps, 

 and in this condition are capable of simple osmotic transmission 

 into the bloodvessels or lacteals. However, the greater portion 

 of the fat enters the lacteals as such in a condition of a fine emul- 

 sion, i.e., composed of solid particles. This process is difficult to 

 reconcile with our physical experiences; for, however finely 

 divitlt <1 it may be, fat emulsified does not pass through an animal 

 membrane more freely than ordinary fluid fat. The fat emulsion 

 is chiefly taken up by the villi of the small intestines, as in the 

 stomach it exists only in large fluid masses or globules, and the 

 amount of fat found in the large intestine is small, unless used as 

 food in great excess. This can also be seen in examining the ab- 

 sorbent vessels after a fatty meal when those which carry mate- 

 rials from the stomach and large intestine are clear and trans- 

 parent, while those coming from the small intestines are filled 

 with the white milky fluid which gives them their special name 

 of lacteals. There is a limit to the absorbent capacity of the 

 intestine for fatty matters, for when a great excess of fat is eaten 



