INTRODUCTION. 21 



these masses that the mind perceives : there may also be real sensa- 

 tions, without the external organ being affected, which originate 

 either in the nervous chain of communication, or in the central mass 

 itself ; such are dreams and visions, or certain accidental 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. Let us trace 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 impres- 

 sions 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, extent, 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 different 

 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, expe- 

 rience and repeated essays soon show what movements are required to 

 procure the one and avoid the other ; and with respect to this, the 

 intelligence abstracts itself from the general rules to direct the will. 



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

 and vice versa, the subsequent sensations become associated with the 

 idea of the primitive one, and modify the general rules framed by intel- 

 ligence this is prudence. 



From the application of these rules to general ideas, result certain 

 formulae, which are afterwards easily adapted to particular cases this 

 is called reasoning. 



A lively remembrance of primitive and associated sensations, and of 



