296 ALL ANIMAL MATTER VALUABLE AS MANURE. 



it has to be remembered that although carbonic acid 

 and ammonia are the principal food of plants, yet 

 that there are limits to the quantity of these sub- 

 stances they can absorb, and that too great a supply 

 of such food is not only useless, but objectionable, 

 and even highly injurious. It is useless to give a 

 plant abundance of carbonic acid and ammonia, if 

 we do not at the same time give it those earthy and 

 saline substances which it requires (654). Even if 

 both are supplied to plants, it is impossible for them 

 to absorb more than a limited quantity. Excess does 

 harm (745). 



785. As animal matter is either directly or in- 

 directly formed from vegetable substances, it is 

 natural to expect that animal substances must con- 

 tain, in addition to the four elements of organic 

 matter (556), the same earthy substances which plants 

 contain, and this is really the fact (595). The phos- 

 phate and carbonate of lime of the bones is obtained 

 from plants, and the alkaline and other salts found 

 in the various parts of the animal body are derived 

 from a similar source. 



786. The knowledge of this fact necessarily leads 

 to the conclusion that all animal matter must be val- 

 uable as manure. The flesh and softer parts of ani- 

 mals, as well as the bones and other solids of the 

 body, are composed of the same substances, both 

 inorganic and organic, as plants ; and during their 

 putrefaction yield them up again in a fit state to 

 be absorbed by plants. 



