212 ZOOLOGICAL PHILOSOPHY 



nature, they sought it beyond her ; they imagined a vital principle, a 

 perishable soul for animals, and even attributed the same to plants ; 

 thus in place of positive knowledge, which they could not attain from 

 want of observations, they created mere words to which are attached 

 only vague and unreal ideas. 



Whenever we abandon nature, and give ourselves up to the fan- 

 tastic flights of our imagination, we become lost in vagueness, and 

 our efforts culminate only in errors. The only knowledge that it is 

 possible for us to acquire is and always will be confined to what we have 

 derived from a continued study of nature's laws ; beyond nature all 

 is bewilderment and delusion : such is my belief. 



If it were true that it is really beyond our powers to ascertain the 

 exciting cause of organic movements, it would be none the less obvious 

 that such a cause exists and that it is physical, since we can observe its 

 effects and nature has all the means of producing it. Do we not know 

 that it spreads and maintains movement in all bodies, and that none 

 of the objects submitted to nature's laws really possesses an absolute 

 stability ? 



I do not wish to go back to the consideration of fiirst causes, nor of 

 all the movements and changes observed in physical bodies of all 

 kinds. We shall confine ourselves to a study of the immediate re- 

 cognised causes acting on living bodies, and we shall see that they 

 are quite sufficient to maintain in these bodies the movements 

 constituting life, so long as the appropriate order of things is not 

 destroyed. 



It would doubtless be impossible to ascertain the exciting cause of 

 organic movement if the subtle, invisible, uncontainable, incessantly 

 moving fluids which constitute it were not disclosed to us in a great 

 variety of circumstances ; if we had not proofs that the whole environ- 

 ment in which all living bodies dwell are permanently filled with them ; 

 lastly, if we did not know positively that these invisible fluids penetrate 

 more or less easily the masses of all these bodies and stay in them for a 

 longer or shorter time ; and that some of them are in a constant 

 state of agitation and expansion, from which they derive the faculty 

 of distending the parts in which they are insinuated, of rarefying the 

 special fluids of the living bodies that they penetrate, and of com- 

 municating to the soft parts of these same bodies, an erethism or 

 special tension which they retain so long as their condition is 

 favourable to it. 



But it is well known that the question at issue is not insoluble ; 

 for no part of the earth inhabited by living beings is destitute of 

 caloric (even in the coldest regions), of electricity, of magnetic fluid, 

 etc. These fluids, some of which are expansive and the others agitated 



