COMPOSITION OF FERTILE SOILS. 141 



small quantities of it. The production of flesh and 

 fat may be artificially increased; all domestic 

 animals, for example, contain much fat. We give 

 food to animals, which increases the activity of 

 certain organs, and is itself capable of being trans- 

 formed into fat. We add to the quantity of food, or 

 we lessen the processes of respiration and perspira- 

 tion by preventing motion. The conditions neces- 

 sary to effect this purpose in birds are different 

 from those in quadrupeds ; and it is well known 

 that charcoal powder produces such an excessive 

 growth of the liver of a goose, as at length causes 

 the death of the animal. 



The increase or diminution of the vital activity 

 of vegetables depends only on heat and solar light, 

 which we have not arbitrarily at our disposal : all 

 that we can do is to supply those substances which 

 are adapted for assimilation by the power already 

 present in the organs of the plant. But what then 

 are these substances ? They may easily be detected 

 by the examination of a soil, which is always fer- 

 tile in given cosmical and atmospheric conditions ; 

 for it is evident, that the knowledge of its state and 

 composition must enable us to discover the circum- 

 stances under which a sterile soil may be rendered 

 fertile. It is the duty of the chemist to explain 

 the composition of a fertile soil, but the discovery 

 of its proper state or condition belongs to the agri- 

 culturist ; our present business lies only with the 

 former. 



