206 ZOOLOGICAL PHILOSOPHY 



and the various fluids of which undergo movements, displacements, 

 dissipations, subsequent renewals, changes of state, and finally deposit 

 parts which become fixed there. We shall then observe that an 

 exciting cause of varying activity, but never entirely absent, in- 

 cessantly animates the very supple containing parts of these bodies, 

 as well as the essential fluids contained in them, and that this cause 

 keeps up all the movements constituting active life, so long as the parts 

 which have to acquire these movements are in a condition to do so. 



Inference. 



The order of things necessary for the existence of life in a body is 

 then essentially as follows : 



1. A cellular tissue (or organs formed of it) endowed with great 

 suppleness and animated by orgasm, the first result of the exciting 

 cause ; 



2. Various more or less complex fluids contained in this cellular 

 tissue (or in the organs built up from it), and undergoing as a second 

 result of the exciting cause, movements, displacements, various 

 changes, etc. 



In animals the exciting cause of organic movements acts powerfully 

 both on the containing parts and on the contained fluids ; it maintains 

 an energetic orgasm in the containing parts, puts them in a condition 

 to react on the contained fluids and hence makes them highly irritable ; 

 as to the contained fluids, the exciting cause involves them in a kind of 

 rarefaction and expansion, which facilitate their various movements. 



In plants, on the contrary, the exciting cause in question only acts 

 powerfully on the contained fluids, and produces in these fluids such 

 movements and alterations as they are adapted to undergo ; but its 

 only eff"ect on the containing parts of these living bodies, even on their 

 most supple parts, is an orgasm or slight erethism which is too feeble 

 to permit of any movement or to cause a reaction on the contained 

 fluids or consequently to endow these parts with irritability. The 

 result of this orgasm has been badly named latent sensibility ; I shall 

 speak of it in Chapter IV. 



In animals, which invariably have parts that are irritable, the vital 

 movements are kept up in some solely by the irritabihty of the parts, 

 and in others by a combination of irritability with muscular activity 

 of the organs themselves. 



In fact, in those animals whose very simple organisation only requires 

 slow movements in the contained fluids, the vital movements are carried 

 out exclusively through the irritability of the containing parts and the 

 agitation produced by the exciting cause in the contained fluids. But 

 as the vital energy increases in proportion to complexity of organisa- 



