264 ZOOLOGICAL PHILOSOPHY 



true that nutrition gradually provides the parts with more soUd sub- 

 stances than fluid and volatile substances ; it will follow that the organs 

 will gradually acquire increasing rigidity, making them less fitted for 

 carrying out their functions, as is actually the case. 



It is far from being true that the whole environment of living bodies 

 tends to their destruction, as is repeated in all modern physiological 

 works. I am convinced that, on the contrary, they only maintain 

 their existence by means of external influences, and that the cause 

 leading to the death of the individuals is within them and not without 

 them. 



Indeed I see clearly that this cause is due to the difference between 

 the substances assimilated and fixed by nutrition, and those thrown 

 out or dissipated by the continual wastage to which living bodies are 

 subject, since volatile substances are always the first and the easiest 

 to be freed from their state of combination. 



I see, in short, that this cause, which brings about old age, decrepi- 

 tude, and finally death, resides in the progressive hardening of the 

 organs ; a hardening which gradually produces rigidity, and which 

 in animals reduces to a corresponding extent the intensity of orgasm 

 and irritability, stiffens and narrows the vessels, and imperceptibly 

 destroys the action of the fluids on the solids, and vice versa. Lastly, 

 it disturbs the order and state of things necessary to life, which 

 ultimately is entirely extinguished. 



I believe I have proved that the faculties common to all living 

 bodies are those of feeding ; of building up for themselves the various 

 substances of which their bodies are composed ; of developing and 

 growing up to a certain limit that varies in each case ; of propagating, 

 that is, of reproducing other individuals like themselves ; lastly, of 

 losing their life by a cause that is within themselves. 



I shall now examine the faculties that are peculiar to some living 

 bodies ; and shall confine myself, as I have just done, to an exposition 

 of the general facts without any attempt to enter into the details that 

 may be found in works on physiology. 



