CHAPTER III. 



DIGESTION AND RESORPTIOK 



§ 1. DiGESTIOK. 



Introdtictory. — Tlie nutrients described in tlie preced- 

 ing chapter, as they occur in the ordinary fodders, are not 

 in suitable condition to become at once part of the body. 

 They must be separated from the various useless substan- 

 ces with which they are associated, and be converted into 

 soluble forms, befoie they can be taken up into the circula- 

 tion and so serve to nourish the body ; — that is, they must 

 be digested. ' 



" The digestive apparatus has been compared to the fit- 

 tings of a pharmaceutist's laboratory in which extracts are 

 prepared from organic substances. As, theie, the mass to 

 be extracted is pulverized by mortars, rasps, knives, and 

 similar tools, so are the feeding-stuffs by the teeth of the 

 animal ; what is effected there by water, alcohol, ether, and 

 other extracting fluids, tlie digestive juices which are se- 

 creted by various glands, and with which the whole mass 

 to be digested is saturated, do in the animal body. 



" As, in the laboratory, the sufficiently extracted materials 

 are filtered to obtain the finished extract, so the filtration 

 of the extracted nutrients in the animal body takes place 

 through the membranes of the intestines. 



^' In the laboratory, the finished extract is received into a 

 suitable vessel, and the worthless residue is thrown away ; 

 in tlie body, the blood and lymph vessels receive the ex- 



