OF URINE. 189 



We cannot ascribe much of the power of the ex- 

 crements of black cattle, sheep, and horses, to the 

 nitrogen which they contain, for its quantity is too 

 minute. But that contained in the faeces of man is 

 proportionably much greater, although by no means 

 constant. In the faeces of the inhabitants of towns, 

 for example, who feed on animal matter, there is 

 much more of this constituent than in those of peas- 

 ants, or of such people as reside in the country. 

 The faeces of those who live principally on bread and 

 potatoes are similar in composition and properties to 

 those of animals. 



All excrements have in this respect a very varia- 

 ble and relative value. T-hus those of black cattle 

 and horses are of great use on soils consisting of 

 lime and sand, which contain no silicate of potash 

 and phosphates ; whilst their value is much less when 

 applied to soils formed of argillaceous earth, basalt, 

 granite, porphyry, clinkstone, and even mountain- 

 limestone, because all these contain potash in con- 

 siderable quantity. In such soils human excrements 

 are extremely beneficial, and increase their fertility 

 in a remarkable degree ; they are, of course, as ad- 

 vantageous for other soils also; but for the manure 

 of those first mentioned, the excrements of other 

 animals are quite indispensable. 



OF URINE. 



We possess only one other natural source of ma- 

 nure which acts by its nitrogen, besides the faeces 

 of animals, — namely, the urine of man and animals. 



Urine is employed as a manure either in the liquid 

 state, or with the faeces which are impregnated with 

 it. It is the urine contained in them which gives to 

 the solid faeces the property of emitting ammonia, — 

 a property v/hich they themselves possess only in a 

 very slight degree. 



When we examine what substances we add to a 



