46 THE DATA OF BIOLOGY. 



actions thus caused, are sa great in their amounts compared 

 with the direct re-actions, that they quite obscure them. 



The impossibility of separating tliese two kinds of re- 

 action compels us to disregard the distinction between them. 

 Under the above general title, we must include both the im- 

 mediate re-actions and those re-actions mediately produced, 

 which are among the most conspicuous of vital phenomena. 



§ 18. From organic matter, as from all other matter, in- 

 cident forces call forth that re-action which we know as 

 heat. More or less of molecular vibration necessarily results 

 when, to the forces at work among the molecules of any 

 aggregate, other forces are added. Experiment abundantly 

 demonstrates this in the case of inorganic masses; and it 

 must equally hold in the case of organic masses. In 



both cases the force which, more markedly than any other, 

 produces this thermal re-action, is that which ends in the 

 union of different substances. Though inanimate bodies ad- 

 mit of being greatly heated by pressure and by the electric 

 current, yet the evolutions of heat, thus induced are neither 

 so common, nor in most cases so conspicuous, as those result- 

 ing from chemical combination. And though in animate 

 bodies there are certain amounts of heat generated by other 

 actions, yet these are secondary to the heat generated by the 

 action of oxygen on the substances composing the tissues and 

 the substances contained in them. Here, however, 



we see one of the characteristic distinctions between inani- 

 mate and animate bodies. Among the first there are but 

 few which ordinarily exist in a condition to evolve the heat 

 caused by chemical combination; and such as are in this 

 condition soon cease to be so when chemical combination 

 and genesis of heat once begin in them. Whereas, among 

 the second there universally exists the ability, more or less 

 decided, thus to evolve heat; and the evolution of heat, in 

 some cases very slight and in no cases very great, continues 

 as long as they remain animate bodies. 



