12 BIOLOGY. [BOOK i. 



If the results are accepted of elementary chemical analysis by 

 decomposition, organised beings do not differ in substance from 

 unorganised beings. But the analogy in substance does not 

 exclude very important differences in form ; for we know that 

 the properties of bodies are intimately related to their com- 

 position, to the mode of aggregation of the substances which 

 constitute them. 



Let us remark, in passing, that of the four simple bodies 

 occupying the first place in the composition of the body of man 

 and of the animals, there are two whose affinities of combination 

 are neither strong nor numerous, and which have a certain degree 

 of chemical inertia. Carbon, which is completely inert in 

 ordinary temperatures, unites itself only to a small number of 

 substances, and often by only a feeble bond. Nevertheless it 

 largely blends with the constitution of plants, and occupies a 

 very important place in the constitution of animals. Azote, 

 more indifferent still than carbon, is found in large quantities in 

 the vegetal kingdom, in quantities still larger in the animal 

 kingdom. It is this very inertia shared, though in a less degree 

 by a third element, hydrogen, which renders these bodies suit- 

 able to figure in the chemical constitution of living beings. 1 In 

 these beings, in effect, matter is in a state of extreme mobility ; 

 it is subject to a perpetual movement of combination and decom- 

 bination ; without repose, without truce, its elements go and 

 come, have reciprocities of action, aggregate themselves, dis- 

 aggregate themselves ; there is a real whirl of atoms, in the very 

 midst of which fixed compounds, with chemical elements solidly 

 cemented together, can only figure in a secondary fashion. Here 

 are needed compounds unstable, of a great molecular mobility, 

 capable of forming, disaggregating, metamorphosing, themselves, 

 of renewing the woof of the living tissues. 



At the very outset the ternary compounds non-azotised, the 



aggregates of hydrogen, of oxygen, and of carbon, that is to say, 



the fixed oils, the fats, the gums, the starches, the resins, the 



sugars, and so on, the constituent principles of plants and 



1 See H. Spencer, The Principles of Biology, vol. i. 



