HOW Tin: ANIMAL LIVES 213 



restricted. The intestine ot" tlio ox is about Itio 

 feet longr, tliat of tlic hoi-se 90 feet, aud tliut 

 of the dog only 111 to 14 feet, 



'2b. Food constifunits 



.')(j!>. All foods must contain clu'iuical ('<iii- 

 stitu«'nts which will serve to repair the waste of 

 the body, to develoj) growing tissue, aud to suj)- 

 ply materials for the ditlcrcnt secretions. 



370. Aside from mineral matters, all food 

 constituents which can build uj) the tissues nuist 

 contain nitrogen, the element which forms four- 

 lifths of the atmosphere, an<l which is an e>>iii- 

 tial part of all body tissues. As familiar ex- 

 amples of su»'li nitrogenous foo<ls or aliments 

 may be named white of ofxg (albumin), milk 

 curd (casein), aud one of the soluble parts of 

 flour (gluten). 



371. As common fornis of foods that contaip 

 no nitrogen, and which cannot form tissues, art. 

 starch, sugar and fats. These are used up or 

 l>urne<l in the syst«Mn to j)ro<iuce bo<ly lieat, to 

 stinudate the contraction of musides, and to fur- 

 nish secretions which are free from nitrogen, 

 such as sugar and butter-fat in milk, and sugar 

 (more propeily glycogen or sugar-forrnei) in the 

 liver. 



37'J. Both sugar and fat, however, can be 

 formed in the body from nitrogenous foo<l, as 



