THE PRINCIPLES OP BIOLOGY. 
99 
THE PKINCIPLES OF BIOLOGY. 
BY HERBERT SPENCER. 
EXPOSITION OF CHAPTER III. 
The Re-actions of Organic Matter on Forces. 
BY FREDERICK JOHN CULLIS. 
This chapter is very intimately related to the two 
preceding ones, concluding the argument opened in them. 
In Chapter I. some important aspects of the physical and 
chemical composition of organic and organisable matter are 
considered, and it is found that such matter is extremely 
susceptible of change. Chapter II. discusses the action of 
force on these changeable substances, and shows how, in the 
leaves of plants, matter is compounded into potential forms 
bv the accumulated effect of multitudes of infinitesimal 
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etlierial impacts ; and that in the tissues of animals, under 
the catalytic action of ferments, these complex bodies are 
again reduced to simpler forms. In Chapter III. we are 
shown that these changes of matter are accompanied by 
equivalent changes of force. Perfect symmetry of the argu¬ 
ment would have demanded a discussion of that accumulation 
of energy which accompanies the building up of food-stuffs 
in the green parts of plants, and of the manifestations of 
force which result from the decomposition of matter in the 
tissues of animals. But only the latter series of phenomena 
are considered on this side of the argument. 
It is shewn successively that this manifestation of force 
occurs— 
(a.) As heat. It being a chief characteristic of animate 
bodies that they maintain a constant evolution of 
heat, the quantity of which is strictly dependent 
on the amount of organic matter decomposed 
by the organism. 
(b.) As light. Though less conspicuously than heat, light 
also is sometimes given off by animals as a partial 
result of the liberation of force in their tissues; 
the phosphorescence of some insects and marine 
animals being well-known phenomena. 
(c.) As electricity. Which is found to be constantly 
generated in the ordinary structures of the higher 
animals, as well as in the special organs of electric 
fishes. 
