INTRODUCTION 185 



It is apparently reflections of this kind which caused Condillac to 

 say that " reason has very little force and makes very slow progress, 

 when it has to destroy errors from which no one is exempt " {Tra/iU 

 des Sensations, vol. i., p. 1108). 



M. Cabanis unquestionably estabUshed a very great truth by a 

 series of unexceptionable facts, when he said that the moral and the 

 physical both spring from a common origin ; and when he showed that 

 the operations called moral are directly due, like those called physical, to 

 the activity either of certain special organs, or of the hving system as a 

 whole ; and, finally, that all the phenomena of intelligence and will take 

 their origin from the congenital or fortuitous state of the organisation. 



But in order to see more clearly how firmly this great truth is based, 

 we must not confine ourselves to seeking the proofs of it by an examin- 

 ation of the highly complicated organisation of man and the more 

 perfect animals ; proof will be obtained still more easily by studying 

 the diverse progress in complexity of organisation from the most 

 imperfect animals up to those whose organisation is the most complex ; 

 for this progress will then exhibit in turn the origin of every animal 

 faculty and the causes and developments of these faculties. We 

 shall then acquire a renewed conviction that those two great branches 

 of our existence called the physical and the moral, which exhibit two 

 orders of phenomena apparently so distinct, have a common basis in 

 organisation. 



This being so, it is in the simplest of all organisations that we should 

 open our inquiry as to what life actually consists of, what are the 

 conditions necessary for its existence, anSTIf om wEatlource it derives 

 the special force which stfmulates the movemenfe called vital. 



As a matter ^f fact it is only hj a study of the simplest organisa- 

 tions that we can attain a knowledge of the true conditions for the 

 existence of hfe in a body ; for in a complex organisation all the principal 

 internal organs are necessary for the maintenance of life on accoimt 

 of their close connection with other parts of the system, and because 

 the system itself is formed on a plan which requires these organs ; 

 but it does not follow that these same organs are essential to the 

 existence of life in all living bodies whatsoever. 



This is very important to remember when we are enquiring what 

 are the real conditions for the constitution of life ; otherwise we might 

 thoughtlessly attribute to some special organ an existence that is 

 indispensable for the manifestations of hfe. 



The pecuUarity of vital movementejs to be started and maintained 

 by stiinialua-andjlQi.^y transmission. These movements are the only 

 ones of this character in nature, except perhaps for those of fermenta- 

 tion ; they differ however from the movements of fermentation in 



