CHAPTER IV. 



ABSORPTION. 



ACCORDING to some authors, the absorption of the economy in its 

 entirety consists of two processes, the first of \rhich has for its pur- 

 pose and aim the introduction into the blood-stream of fresh material, 

 for the nutrition of the various tissues of the body. It is called ab- 

 sorption from without, and has its seat in the alimentary canal chiefly, 

 aided, to some extent, by the skin and lungs. The second process 

 endeavors to remove from the numerous tissues of the body, by very 

 gradual measures, the waste-products that would otherwise accrue 

 everywhere within the body, as a resultant of the use of its various 

 tissues. This second process is known as the absorption that takes 

 place from within, and has its seat everywhere within the tissues of 

 the body. 



For many years the old physiologists entertained the view that 

 absorption of the end-products of digestion from the alimentary 

 canal was purely physical; that is, that the same laws governed this 

 bodily function that do the passage of any liquid, with its contained 

 dissolved substances, through a dead membrane placed outside of the 

 body. These processes of osmosis and filtration, as they were known 

 to the physicist, are to a small extent responsible for some of the 

 intestinal absorption. But to-day the newer view concerning this 

 absorption is accepted, whereby it is believed that the living epithelial 

 cells of the lining mucous membrane of the small intestine possess in 

 themselves, as living beings, the power to exert a selective action dur- 

 ing absorption ; at the same time, they modify the end-products dur- 

 ing their passage through them. They change the peptones into al- 

 bumins, and unite the fatty acids to glycerin. That the process was 

 selective, and not due to purely physical laws, was proved by the more 

 rapid absorption of grape-sugar than sodium sulphate, though the 

 latter was many times more diffusible than the former. 



OSMOSIS. 



Ions. 



An electrolyte is a chemical compound which, when molten or in 

 solution, conducts an electrical current. When such a current passes 

 through its solution, the latter undergoes certain changes that are 

 grouped under the name of electrolysis. The places at which the 



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