128 ON WHAT THE VALUE OF FOOD DEPENDS 



obtained by Dr. Wolff in Saxony, given as a means of 

 comparison. 



ir. 



in. 



iv. 



v. 



Johnson also remarks, in this connection, that the 

 great value of linseed-cake, as an adjunct to hay for fat 

 cattle and milch cows, has long been recognized ; and 

 is undeniably traceable in the main to three ingredients 

 of the seeds of the oil-yielding plants. The value of 

 food depends upon the quantity of matters it contains 

 which may be appropriated by the animal which con- 

 sumes the food. Now, it is proved that the fat of ani- 

 mals is derivable from the starch, gum, and sugar, and 

 more directly and easily from the oil of the food. 

 These four substances are, then, the fat-formers. The 

 muscles, nerves, and tendons of animals, the fibrine of 

 their blood, and the curd of their milk, are almost iden- 

 tical in composition, and strongly similar in many of 

 their properties with matters found in all vegetables, 

 but chiefly in such as form the most concentrated food. 

 These blood (and muscle) formers are characterized by 

 containing about fifteen and a half per cent, of nitrogen ; 

 and hence are called nitrogenous substances. They are 

 also often designated as the albuminous bodies. 



The bony framework of the animal owes its solidity 

 to phosphate of lime, and this substance must be fur- 



