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 what point they reach in each being, and assure himself whether 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 affected, and which 
originate either in the nervous passage, 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, 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 the brain and the whole of the medulla, 
and 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 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 impressions 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 object presents itself to the memory with all its qualities, or wdth all its 
accessory ideas. 
Intellect has the power of separating these accessory ideas of objects, and of com- 
bining those that are alike 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 the 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 
