[395] SCIENTIFIC MANUAL. 109> 



version of the secondary products of the natural manufac- 

 ture of the third class, such as butter, cheese, etc. 



"Man, and all domestic animals, may be supported, may 

 even be fattened, upon vegetable food alone. Vegetables, 

 therefore, must contain all the substances which are neces- 

 sary to build up the several parts of animal bodies, and to 

 supply the waste attendant upon the performance of the 

 necessary functions of animal life." Elements of Ag'l 

 Ch. and Geol'y. Johnston. 



Indeed the composition of animal substances may be in- 

 ferred from that of mixed vegetation, since animals that 

 live upon such food, must build up their frames entire- 

 ly from that source, by simple digestion and assimila- 

 tion. Vegetation must not only supply the carbon of 

 the fat, the fibrin of the muscles, the saline matters 

 of the blood, and the gelatine of the skin, hair, horns, 

 hoofs, and bones, but must furnish the earthy matters of 

 the bones of animals. 



"It is a wise, and beautiful provision of nature, there- 

 fore, that plants are so organized as to refuse to grow in 

 a soil from which they cannot obtain an adequate supply 

 of soluble inorganic food since that saline matter, which 

 ministers first to their own wants, is afterwards surren- 

 dered by them to the animals they are destined to feed. 



"Thus the dead earth and the living animal are but parts 

 of the same system links in the same endless chain of 

 natural existences. The plant is the connecting bond by 

 which they are tied together on the one hand the decay- 

 ing animal matter, which returns to the soil, connects them 

 on the other." Ag'l Ch. and Geol'y Johnston. 



There are two classes of substances in plants known to 

 chemists as albuminoids and carbo-hydrates, the former em- 

 bracing the flesh-forming principles of the food of ani- 

 mals ; the latter the fat and heat producing principles. 



The ratio of these substances should vary according to 



