ARTIFICIAL MANURING. 137 



in the body of the animals, and served to increase their 

 weig-ht, are found ag-ain in the hones and excrements of man 

 "who consumes the flesh of these animals. 



The excrements of man contain the elements of the soil, of 

 bread or of grain, of veg-etables and meat. 



These discoveries explain, in a most simple and satisfac- 

 tory manner, the fertilizing- effect which manure produces on 

 our fields. 



It is now obvious why manure renders again fertile the 

 exhausted fields ; why by its means their productiveness can 

 be augmented; why the latter is in a direct ratio to the 

 quantity of manure administered. 



The exhaustion of the soil by subsequent crops — its 

 decrease in fertility — is produced by the gradual removal of 

 the mineral elements, in a soluble state, which are necessary 

 for the development of our cultivated plants. By a suj)ply 

 of manure they are again restored to that state suited to 

 serve as noiu-ishment to a new vegetation. If the supply of 

 the removed elements of the soil, by means of manure, be 

 sufficient ; if the quantity taken away be restored, the 

 original fertility re-appears ; if the supply be greater, the 

 produce increases ; a defective supply gives a smaller produce. 



It is now explained why the different kinds of manure 

 exercise an unequal effect upon the fields. 



The excrements of man, and the guano, containing espe- 

 cially the mineral ingredients of grain and meat, exercise far 

 greater influence on the amount of produce in grain in a 

 field in which these ingredients are wanting, even if those of 

 the leaves and stalks are present in sufficient quantity, than, 

 the excrements of an animal which feeds on roots or green 

 fodder. The excrements of the latter contain the mineral 

 elements of the leaves, stalks, and roots, in prevailing quan- 

 tity, and have a greater value for the production of roots and 

 foliaceous plants than those of man or birds, which contain 

 only a small quantity of those mineral substances which 

 they require for their development. 



If we compare, for instance, the composition of guano 

 with the excrements of the cow — solid and fluid excrements 

 in the same state of dryness — it is found, that in an equal 

 weight the latter contain five to seven times more of the 

 mineral ingredients of turnii)s and potatoes than the former. 

 If, in a soil which is deprived of all these mineral sub- 

 stances, we Avish to force a crop of turnips by means of 

 guano, we require at least five times more of guano than 

 duno- of cattle. 



