PREFACE 5 



that this inner feeling constituted a power which it was essential to 

 take into consideration. 



Nothing in fact seems to me so important as the feeling which I 

 have named, considered both in man and in the animals which possess 

 a nervous system capable of producing it. It is a feeUng which can 

 be aroused by physical and moral needs, and which becomes the source 

 whence movements and actions derive their means of execution. 

 No one that I know had paid any attention to it ; and this gap in our 

 knowledge of one of the most powerful causes of the principal pheno- 

 mena of animal organisation rendered all explanations inadequate 

 to account for these phenomena. We have, however, a sort of clue 

 to the existence of that inner power when we speak of the agitations 

 which we ourselves are constantly experiencing ; for the word emotion, 

 which I did not create, is often enough pronounced in conversation 

 to express the observed facts. 



When I had considered that the inner feeling was susceptible of 

 being arou,sed by different causes, and that it then constituted a 

 power capable of exciting actions, I was so to speak struck by the 

 multitude of known facts which attest the actual existence of that 

 power ; the difficulties which had long puzzled me with regard to the 

 exciting cause of actions appeared to me entirely surmounted. 



Admitting that I had been fortunate enough to aUght upon a 

 truth in attributing to the inner feeling of animals which have it the 

 power which produces their movements, I had still only surmounted 

 a part of the difficulties by which this research is hampered. For 

 it is obvious that not all known animals do or can possess a nervous 

 system ; consequently, all animals do not possess the inner feeling 

 of which I am speaking ; and in the case of those which are destitute 

 of it, the movements which they are seen to execute must have another 

 origin. 



I had reached this point when I reflected that without internal 

 excitations plant life would not exist at all, nor be able to maintain 

 itself in activity. I recognised the fact that the same consideration 

 appUed to a large number of animals ; and as I had very frequently 

 observed that nature varies her means when necessary in order to 

 attain the same end, I had no further doubt about the matter. 



I think therefore that the very imperfect animals which have no 

 nervous system live only by the help of excitations which they receive 

 from the exterior. That is to say, subtle and ever moving fluids 

 contained in the environment incessantly penetrate these organised 

 bodies and maintain life in them, so long as the state of these bodies 

 permits of it. Now this thought is one which I have many times 

 considered, which many facts appear to me to confirm, against which 



