30 INTRODUCTION. 



communication between the external sense and the central masses 

 of the medullary system. It is then the modification only expe- 

 rienced by these masses that the mind perceives: there may also be 

 real sensations, without the external organ being affected, and which 

 originate either in the nervous chain of communication, or in the 

 central mass itself; such are dreams and visions, or certain acci- 

 dental sensations. 



By central masses, we mean a part of the nervous system, that is 

 so much the more circumscribed, as the animal is more perfect. In 

 Man, it consists exclusively of a limited portion of the brain; but in 

 Reptiles, it includes the brain and the whole of the medulla, and of 

 each of their parts taken separately, so that the absence of the 

 entire brain does not prevent sensation. In the inferior classes this 

 extension is still greater. 



The perception acquired produces the image of the sensation 

 experienced. We trace to without the cause of that sensation, and 

 thus acquire the idea of the object that has produced it. By a 

 necessary law of our intelligence, all ideas of material objects are 

 in time and space. 



The modifications experienced by the medullary masses leave 

 impressions there which are reproduced, and thus recal to the mind 

 images and ideas; this is memory, a corporeal faculty that varies 

 greatly, according to the age and health of the animal. 



Similar ideas, or such as have been acquired at the same time, 

 recal each other; this is the association of ideas. The order, ex- 

 tent and quickness of this association constitute the perfection of 

 memory. 



Every object presents itself to the memory with all its qualities or 

 with all its accessary ideas. 



Intelligence has the power of separating these accessary ideas 

 of objects, and of combining those that are alike in several differ- 

 ent objects under a general idea; the object of which no where 

 really exists, nor presents itself per se this is abstraction. 



Every sensation being more or less agreeable or disagreeable, 

 xperience and repeated essays soon show what movements are re- 

 uired to procure the one and avoid the other; and with respect to 

 his, the intelligence abstracts itself from the general rules to direct 

 he will. 



An agreeable sensation being liable to consequences that are not 

 so, and vice versa, the subsequent sensations become associated with 



