186 ZOOLOGICAL PHILOSOPHY 



that they can be maintained almost unchanged for a limited period, 

 and in that they lead to a growth subsequently maintained for some 

 time of the body in which they work, whereas those of fermentation 

 irreparably destroy the body subjected to it and increase up to the 

 limit that annihilates them. 



Since vital movements are never transmitted but always stimulated, 

 we must enquire what is their exciting cause, that is to say, from what 

 source living bodies derive the peculiar force which animates them. 



Whatever may be the state of organisation of a body and of its 

 essential fluids, active life could assuredly not exist in that body 

 without a special cause capable of exciting its vital movements. What- 

 ever hypothesis we may form in this matter, we are always obliged to 

 recognise that some special cause must be present for the active mani- 

 festations of life. Now it can no longer be doubted that this cause 

 which animates living bodies is to be found in the environment of those 

 bodies, and thus varies in intensity according to places, seasons, and 

 climates. It is in no way dependent on the bodies which it animates, 

 it exists before they do and remains after they have been destroyed. 

 Lastly, it stimulates in them the movements of life, so long as the state 

 of these bodies allows ; and it ceases to animate them when that state 

 opposes obstacles to the performance of the movements which it 

 stimulates. 



In the most perfect animals this exciting cause of life is developed 

 within themselves, and suffices to animate them up to a certain point ; 

 but it still needs the co-operation of that provided by the environment. 

 In the other animals, and in all plants it is altogether external to them ; 

 so that they can only obtain it from their environment. 



When these interesting facts have been ascertained and settled, 

 we shall enquire how the first outlines of organisation come to be 

 formed, how spontaneous generation can have occurred and in what 

 part of the two series of living bodies. 



If, indeed, bodies which possess life are really productions of nature, 

 she must have had and still have the faculty of producing some of them 

 spontaneously. She must then have endowed them with the faculty 

 of growth, multiplication and increasing complexity of organisation 

 and the power of varying according to time and circumstances. She 

 must have done this if all those that we now observe are really the 

 products of her power and efforts. 



After recognising the necessity for these acts of direct creation, 

 we must enquire which are the living bodies that nature may produce 

 spontaneously, and distinguish them from those which only derive 

 their existence indirectly from her. Assuredly the lion, eagle, butter- 

 fly, oak, rose, do not derive their existence immediately from nature ; 



