70 MANUAL OF CATTLE-FEEDING. 



all the dissolved matter will finally be removed from tlie 

 solution contained in tlie membrane* Substances wLicli 

 are capable of thus passing throngli a membrane are said 

 to be diftusible. 



In tbe body, according to tliis theory of resorption, the 

 intestines constituted the enclosing membrane, the diges- 

 tive fluids converted the nutrients into soluble and diffusi- 

 ble forms, while the blood and lymph of the capillaries 

 and lacteals was the fluid into which diffusion took place. 

 It w^as found that emulsified fats could, by slight pressure, 

 be made to pass through a membrane previously moistened 

 with bile, and on this fact was l)ased the explanation of the 

 resorption of fat, the pressure being supposed to be exerted 

 by the peristaltic movements of the intestines, and the pro- 

 cess of filtration to be aided by a peculiar structure of the 

 villi which kept the lacteals in their centre under a less 

 pressure than was exerted on the outside. In short, re- 

 sorption was believed to consist m diffusion, combined 

 wath filtration under pressure. 



This theory has been extensively held, but the best an- 

 tlijorities now consider it entirely inadequate to explain the 

 known facts of resorption. 



As regards the resorption of fat, the simple fact that the 

 villi are wanting in many of the lower animals, and that 

 these animals nevertheless resorb fat, shows that the sup- 

 posed peculiar structure of the villi is not essential to the 

 process, and a more careful consideration of the anatomy 

 of the intestinal surface shows that the filtration theory is 

 untenable. 



The whole of this surface is covered with the epithelial 

 cells above described, so closely crowded together that any 

 filtration must take place through the semi-fluid proto- 

 plasm of the cells. This protoplasm must behave under 



