208 ZOOLOGICAL PHILOSOPHY 



irritable parts whose reaction could assist its movements. It is enough, 

 as we see in plants, that a body possessing it should present internally 

 an order and state of things with regard to its containing parts and 

 contained fluids which permit of the excitation of the characteristic 

 movements and changes, by means of a special force. 



But if we consider life in special cases, that is, in various selected 

 bodies, we shall then see that whatever is essential to the plan of 

 organisation of these bodies has also become necessary to the main- 

 tenance of hfe in them. 



Thus in man and the most perfect animals, hfe cannot be maintained 

 without irritabihty of the reacting parts, without the involuntary 

 muscles to keep up the rapid movement of the fluids, without the 

 nervous influence which by quite a different route from feehng pro- 

 vides for the performance of the functions of the muscles and other 

 internal organs ; lastly, without the influence of respiration to restore 

 continually the essential fluids which are so rapidly disintegrated 

 in these systems of organisation. 



Now this nervous influence, which is undoubtedly necessary, is 

 exclusively that which sets the muscles in action and not that which 

 produces feehng ; for it is not by means of sensations that the muscles 

 act. In fact, no feehng whatever is aroused by the cause which pro- 

 duces the movements of systole and diastole in the heart and arteries ; 

 and if we do sometimes perceive the beats of the heart it is when they 

 are stronger and more rapid than usual ; this muscle, which is the chief 

 motive power of circulation, then strikes neighbouring sensitive parts. 

 Finally, when we walk or perform any action we never feel the move- 

 ment of the muscles nor the impulse which drives them. 



Hence it is not through the medium of feeling that the muscles 

 carry on their functions, although nervous influence is necessary to 

 them. But since nature was obhged, in order to accelerate the move- 

 ment of fluids in the most perfect animals, to add the muscular move- 

 ment of the heart, etc., to the irritabihty which they possess in conomon 

 with the rest, nervous influence has become necessary to the main- 

 tenance of hfe in these animals. There can, however, be no justiflcation 

 for the statement that their vital movements are only due to impressions 

 received by sensitive parts, for if their irritabihty was destroyed they 

 would immediately lose their hfe ; and their feehng, if it still survived, 

 could not alone sufflce for its preservation. Moreover, I hope to prove 

 in Chapter IV. of this part that sensibility and irritabihty are not 

 only quite distinct faculties, but that they have not even a common 

 origin and are due to very different causes. 



" Living is feehng," said Cabanis : yes, doubtless for man and the 

 most perfect animals and probably too for a great number of inver- 



