MKMOIK XI. J THE FORCE INCLUDED IN PLANTS. 



liglit, and remingling with the universal cosmic force 

 from which it had been of old derived by the sun, or 

 from which, perhaps more correctly speaking, the sun 

 himself was derived, for he is the issue of nebular con- 

 densation. 



I cannot close this Memoir without making reference 

 to a point of surpassing interest. What goes on in the 

 case of a flame, goes on in the case of an animal. Either 

 from other animals or from plants, combustible material 

 is obtained and used as food. Directly or indirectly it 

 undergoes oxidation in the system, brought about by 

 the air introduced through the process of respiration. 

 Speaking in a general manner, though there are many 

 intermediate products, the issue of this chemical action 

 is the evolution of carbonic acid, ammonia, water, which 

 pass into a common receptacle, the atmosphere. Thence 

 their ingredients are taken by plants, and, under the 

 agency of the sunlight, combustible material food is 

 re-formed. The same particle is, therefore, now in the 

 air, now in the plant, now in the animal, now back again 

 in the air. It suffers a perpetual transmigration. 



But in the case of an animal the oxidation may not be 

 so sudden, so complete, as it is in the case of a flame. It 

 may, and indeed generally does, go on stage by stage, 

 step by step, partial oxidations occurring. It is thus 

 that, from one original hydrocarbon, a long catalogue of 

 fatty and oily substances may arise ; the inevitable issue, 

 however, is total oxidation. As the partial degradations 

 go on, in corresponding degrees the latent energy or force 

 is set free. It may assume any correlated form, as mus- 

 cular motion ; or, as heat, it may give warmth to the 

 body; in certain fishes, as the gyinnotus, it may turn 

 into an electrical or nerve current; in certain insects, 

 such as the fire-fly, into light. 



As a cataract is only a form which any river may as- 



