ASSIMILATION OF NITROGEN. 67 



ford, by the emission of these ammoniacal gases, 

 a constant supply of an ingredient necessary 

 for the continual increase of the animal crea- 

 tion. 



To explain the theory of the causes which 

 generate the ammoniacal gases in the bowels 

 of the earth, would be foreign to the purposes 

 of this w^ork. It is sufficient to notice here, 

 their existence and the benefits they are sup- 

 posed to confer on the living organization of 

 the earth.* 



To this cause also, namely the evolution of 

 ammoniacal jgases in the neighbourhood of vol- 

 canoes, Professor Daubeny attributes the lux- 

 uriance which vegetation possesses in all 

 volcanic regions. It may, however, be remem- 

 bered that this luxuriance has already been 

 attributed to the presence of the alkaline pro- 

 perties, which the disintegration of the volca- 

 nic matters in the soil affords to the plant, (page 

 28.) It is possible however and probable, that 

 both these causes united tend to produce this 

 result, which is especially observable in the 

 neighbourhoods of Mount Etna and Vesuvius. 



The effects produced by carbon and nitro- 

 gen on plants, and collaterally on animals, have 

 now been explained, but there is one circum- 

 stance in the assimilation of these substances 

 by animals in their food, which may not be 

 misplaced to notice here. 



It has been before stated that every part of 

 a plant contains nitrogen as well as carbon, but 



* See Daubeny's work " On active and extinct Volcanoes." 



