132 THE BEGINNINGS OF LIFE. 



kingdom, therefore, as a whole,' M. Dumas says, c car- 

 bonic acid, watery vapour, and azote or oxide of ammo- 

 nium are continually escaping simple substances and 

 few in number, the formation of which is intimately 

 connected with the history of the atmosphere itself:' 

 substances, too, which plants are continually needing, 

 and are as continually abstracting from the air. M. 

 Dumas also says : c It is in plants, consequently, that 

 the true laboratory of organic nature resides ; carbon, 

 hydrogen, ammonium, and water are the elements they 

 work upon ; and woody fibre, starch, gums, and sugars, 

 on the one hand, fibrine, albumen, caseum, and gluten, 

 on the other, are the products that present themselves 

 as fundamental in either organic kingdom of nature 

 products, however, which are formed in plants^ and in 



of those molecular changes that are ever going on throughout the living 

 tissues ; or whether the oxygen, playing the part of scavenger, merely 

 aids these changes by carrying away the products of decomposition 

 otherwise caused ; it remains equally true that these changes are main- 

 tained by its instrumentality. Whether the oxygen absorbed and dif- 

 fused through the system effects a direct oxidation of the organic colloid 

 which it permeates ; or whether it first leads to the formation of simpler 

 and more oxidized compounds, that are afterwards further oxidized and 

 reduced to still simpler forms; matters not in so far as the general 

 result is concerned. In any case it holds good, that the substances of 

 which the animal body is built up enter it in a but slightly oxidized and 

 highly unstable state ; while the great mass of them leave it in a fully 

 oxidized and stable state. It follows, therefore, that whatever the 

 special changes gone through, the general process is a falling from 

 a state of unstable equilibrium, to a state of stable chemical equilibrium. 

 Whether this process be direct or indirect, the total molecular re- 

 arrangement and the total motion given out in effecting it must be the 

 same.' (' Principles of Biology,' vol. i. p. 34.) 



