INTRODUCTION. 29 



existence of matter. But the naturalist should examine what appear to be the mate- 

 rial conditions of sensation ; he should trace the ulterior operations of the mind, ascer- 

 tain to wliat point the)' reach in each being, and assure himself whetlier they are not 

 subject to conditions of perfection, dependent on the organization of each species, or 

 on the momentary state of each individual body. 



For the me to perceive, there must be an uninterrupted nervous communication 

 between the external sense and the central masses of the medullary system. Hence it 

 is only when a modification is experienced by these masses that the me perceives : there 

 may also be real sensations, without the external organ being aiFccted, and which 

 originate either in the nervous passage, or in the central mass itself; such arc dreams 

 and visions, or certain accidental sensations. 



By central masses, we mean a part of the ncn'ous sj'stem, which is more circum- 

 scribed as the animal is more perfect. In man, it consists exclusively of a limited 

 portion of the brain ; but in reptiles, it includes tlie brain and the whole of the medulla, 

 and each of their parts taken separately ; so that the absence of the entire brain docs 

 not prevent sensation. In the inferior classes this extension is still greater. 



The perception acquired by the me, produces the image of the sensation ex- 

 perienced. We trace to without the cause of that sensation, and thus acquire the idea 

 of the object which produces it. By a necessary law of our intelligence, all the ideas 

 of material objects are in time and space. 



The modifications experienced by the medullary masses leave imjiressions there, 

 which are reproduced, and recall to mind images and ideas ; this is memory, a cor- 

 poreal faculty that varies considerably, according to age and health. 



Ideas that are similar, or which have been acquired at the same time, recall each 

 other; this is the association of ideas. The order, extent, and promptitude of this asso- 

 ciation constitute the perfection of memory. 



Each obiject presents itself to the memory with all its qualities, or with all its 

 accessory ideas. 



Intellect has the power of separating these accessory ideas of objects, and of com- 

 bining those that are alilve in several different objects under one general idea, the 

 prototype of which nowhere really exists, nor presents itself in an isolated form ; this 

 is abstraction. 



Every sensation being more or less agreeable or disagreeable, experience and re- 

 peated essays show promptly what movements are required to procure the one and 

 avoid the other ; and with respect to this, the intellect abstracts itself from general 

 rules to direct the will. 



An agreeable sensation being liable to consequences that are not so, and vice versd, 

 the subsequent sensations become associated with the idea of the primitive one, and 

 modify the general rules abstracted by the intellect ; this is prudence. 



From the application of rules to general ideas, result certain formulae, which are 

 afterwards adapted easily to particular cases; this is called reasoning — ratiocination. 



A lively remembrance of primitive and associated sensations, and of the impressions 

 of pleasure and pain that attach to them, constitutes imagination. 



One privileged being, Man, has tlie faculty of associating his general ideas with 

 particular images more or less arbitrary, easily impressed upon the memory, and which 

 serve to recall the general ideas which they represent. These associated images are 



