200 DIGESTION. 



NON-NlTROGENOUS : 



(1.) Amyloids Starch, Sugar, and their allies (containing Carbon, 

 Hydrogen, and Oxygen). 



(2.) Oils and Fats (containing Carbon, Hydrogen, and Oxygen; 

 the Oxygen in much smaller proportion than in Starch or Sugar). 



(3 ) Mineral or Saline Matters, as Chloride of Sodium, Phosphate 

 of Lime, &i.-. 



(4 ) Water. 



Animals cannot subsist on any but organic substances, and 

 these must contain the several elements and compounds which 

 are naturally combined with them: in other words, not even 

 organic compounds are nutritive unless they are supplied in 

 their natural state. Pure fibrin, pure gelatin, and other prin- 

 ciples purified from the substances naturally mingled with 

 them, are incapable of supporting life for more than a brief 

 time. 



Moreover, health .cannot be maintained by any number of 

 substances derived exclusively from one only of the two chief 

 groups of alimentary principles mentioned above. A mixture 

 of nitrogenous and non-nitrogenous organic substances, together 

 with the inorganic principles which are severally contained in 

 them, is essential to the well-being, and, generally, even to the 

 existence of an animal. The truth of this is demonstrated by 

 experiments performed for the purpose, and is illustrated by 

 the composition of the food prepared by nature, as the exclu- 

 sive source of nourishment to the young of Mammalia, namely, 

 milk. 



COMPOSITION OF MILK. 



Human. Cows. 



Water, 890 858 



Solids, . . . . . .110 142 



1000 1000 



Casein, 35 68 



Butter, 25 



Sugar (with extractives), 48 30 



Salts, ...... 2 6 



110 142 



In milk, as will be seen from the preceding table, the albu- 

 minous group of aliments is represented by the casein, the 

 oleaginous by the butter, the aqueous by the water, the sac- 

 charine by the sugar of milk. Among the salts of milk are 

 likewise phosphate of lime, alkaline, and other salts, and a 

 trace of iron; so that it may be briefly said to include all the 

 substances which the tissues of the growing animal need for 



