MANURES. 85 



ten, albumen, etc., and that which does not contain 

 nitrogen such as starch, sugar, oil, etc. 



The earthy part of food may also be divided into 

 soluble matter and insoluble matter.* 



DIGESTION AND ITS PRODUCTS. 



Let us suppose that we have a full-grown ox, 

 which is not increasing in any of his parts, but only 

 consumes food to keep up his respiration, and to sup- 

 ply the natural wastes of his body. To this ox we 

 will feed a ton of hay which contains organic mat- 

 ter, with and without nitrogen, and soluble and 

 insoluble earthy substances. Now let us try to fol- 

 low the food through its changes in the animal, and 

 see what becomes of it. Liebig compares the con- 

 sumption of food by animals to the imperfect burning 

 of wood in a stove, where a portion of the fuel is resolv- 

 ed into gases and ashes (that is, it is completely burn- 

 ed), and another portion, which is not thoroughly burn- 

 ed, passes oif as soot. In the animal action in ques- 

 tion, the food undergoes changes which are similar 

 to this burning of wood. A part of the food is di- 

 gested and taken up by the blood, while another por- 

 tion remains undigested, and passes the bowels as 

 solid dung corresponding to the soot of combus- 

 tion. This part of the dung, then, we see is merely 

 so much of the food as passes through the system 



* Xo part of animal manure is permanently and entirely insol- 

 uble. It would perhaps be better to classify these substances as 

 (1) those which are readily soluble, and (2) those which are but 

 slowly soluble. 



