86 EXCREMENTS AND URINE. 



these a few, the alkalies and alkaline salts (potash, 

 soda, common salt, and many others) are readily- 

 soluble ; they must, therefore, be looked for more 

 especially in the urine, whilst those which are insol- 

 uble (to which class, in herbivorous animals, lime, 

 magnesia, silica, and phosphoric acid more particu- 

 larly belong) fall to the share of the solid excre- 

 ments. Thus, for example, of the yearly food of a 

 sheep there pass away, 



By the solid 

 By the urine excrements 



Alkalies and alkaline salts, . 10 2 lbs. 



Common salt, ... 1 55 " 



Lime and magnesia, . . 2J 13 " 



Phosphoric acid, . merely traces 5 " 



Silica, .... merely traces 23 " 



Both kinds of mineral constituents, the soluble as 

 well as the insoluble, are derived from the plants 

 which formed the food of the animal. In these 

 plants their occurrence was not accidental, but ahso- 

 lutely necessary to their very existence ; if, therefore, 

 the faeces of animals are to minister in their turn to 

 the production of fresh plants, they must supply to 

 the latter both kinds of mineral ingredients. A plant 

 enjoys its entire nourishment only when both are 

 presented to it simultaneously, 



2. Constituents of Animal Excrements, and 

 THEIR Value as Manure. 



Since the excrements of our cattle are' derived 

 from the plants which served for their nourishment, 



