MAJ^UAL OF CATTLE-FEEDIWOt. 71 



pressure essentially like a licjuidj that is, it must exert an 

 equal pressure upon all sides of an o]>jeet enclosed in it ; 

 under these circumstances, while diffubion may take place, 

 titration is imposbible. But i£ we admit the impossi- 

 bility of filtration, the whole theory fall-^^, for diiinsion 

 alone would, in many cabos, produce results eutirely dif- 

 ferent from those observed. For example, if water and 

 alcohol be separated by a membrane haviug a greater at- 

 traction for water, the water passes through the mem- 

 brane toward the alcohol faster than the latter passes in 

 the opposite direction, but if alcohol, so diluted as not to 

 injure the epithelium, be introduced into the intestines, it 

 is rapidly resorbed into the blood, while no water passes 

 from the latter into the intestines. 



Moreover, while under normal conditions water is rapidly 

 resorbed, simple irritation of the epithelial cells is suffi- 

 cient to cause the motion to take place m the opposite 

 direction, viz., from the blood into the intestines. 



These and many other considerations force us to the 

 belief that the epithelium of the intestines is the active 

 agent in resorption, and that re.HOQ}tion is a function of 

 the Vimng ^rotojplasm of the ej)ithelkd cells. 



In what manner, or by virtue of what chemical and 

 physical laws, the process takes place, we are ignorant ; and 

 until the relations and properties of protoplasm in general 

 are much better kno\\Ti than at present, it must be regarded 

 as a vain attempt to seek to discover them, nor, indeed, is 

 it important for our present purpose that we should. 



Course of the Nutrients after Resorption. — The 

 substances taken up by the epithelial cells appear to pass 

 from these into the lacteals. Their course from this point 

 is not, in all cases, easily followed, on account of the rapid 

 altei-ation which they undergo. 



