130 THE BEGINNINGS OF LIFE. 



and to those great storehouses of inorganic elements 

 earth, air, and water. 



Whatever be the nature of the functions of the lowest 

 living things, and their relations with the environment, 

 or aqueous medium in which they alone exist, we find, 

 on coming to those more definite organisms which can, 

 without room for doubt, be ranged under either the 

 Animal or the Vegetable Kingdom, that the members 

 of each great class have functions definitely related to 

 one another and to the world of unorganized matter. 



Bearing in mind that the fundamental constituents 

 of living things are carbon, nitrogen, hydrogen, and 

 oxygen, we must also remember that the degree in which 

 other constituents (such as sulphur and phosphorus with 

 various saline materials) enter into the composition of 

 organic matter, is altogether trifling when compared 

 with the immense bulk of living tissue that is almost 

 solely built up of these four elements in their diverse 

 modes of combination. 



We shall then be the better able to appreciate the 

 doctrine so eloquently expounded by the eminent French 

 chemist, M. Dumas, in a work by himself and M. Bous- 

 singault, on c The Chemical and Physiological Balance 

 of Organic Nature.' He calls attention again and again, 

 in the most forcible language, to the all-important com- 

 plemental relation existing between the functions of 

 plants and animals. Plants in their natural and healthy 

 state decompose carbonic acid incessantly, fixing its 

 carbon and setting free its oxygen : similarly they de- 



