MANUAL OF CATTLE-FEEDIJ^a 69 



from tliem. In some cases the substances tliiis resorbed 

 are excreted unchanged ; in others \\6 are able to recognize 

 the prodncts of their decunipubition ^\ithont being able to 

 say exactly where they are destroyed. "Water introduced 

 into the intobtine dibappears, and i;:> excreted xuichanged in 

 the nrine and peispiration; sngar, on the other hand, 

 while it is rapidly resorbed, does not reappear as such, but 

 speedily causes an increased excretion of carbonic acid 

 through the hmgs, showing that it has been oxidized in 

 the body. It woixld seem that only soluble substances are 

 resorbed, both fi^oni the fact that solutions are readily 

 taken up and that the whole digestive process is di- 

 rected toward solution of the solid ingredients of the 

 food. The fats, however, form to a certain extent an 

 exception. We have seen that in the digestive process 

 they are simply eniidsified, and only to a very small extent 

 dissolved. After a meal containing nnich fat, the lacteals 

 are found to be full of a fluid ]ia\ hig a milky appearance 

 which the microscope shows to be due to the prcfeenee of 

 inmnnerable globules of fat, which have evidently been 

 resorbed fi-om the contents of the intebtines, having passed 

 through the epithelial cells. 



Causes of Resorption. — It has been extensively taught 

 that the phenomena of resorption are due chiefly to the 

 action of the laws of the diffusion of liquids through mem- 

 branes, aided by the pressure exerted on the contents of 

 the intestines by the peristaltic motion. 



It is well known that, if solutions of many substances be 

 enclosed in some membrane, like bladder or parchment- 

 paper, and the whole placed in water, the dissolved sub- 

 stance will diffuse through the membrane into the water 

 until the solution is of equal strength on both sides of the 

 membrane, and that, if the water be continually renewed, 



