Cuvierian Sy stein of Zoology, 317 



any direct proof of the actual existence of matter. We are, 

 however, compelled, by an invariable law of the understanding, 

 to refer the objects which excite our sensations to something 

 out of the mind, existing in time or space, to which we give 

 the name of matter, and the naturalist is bound to examine 

 what appear to be the material conditions of sensation. 



In order that external objects may be perceived, it is neces- 

 sary that there should be an uninterrupted nervous communi- 

 cation between the organs of sense, and the central masses of 

 the medullary system ; for it is only the modifications of these 

 masses that are perceived by the mind. 



There may be real sensations, without any impression on 

 the external organs of sense ; these internal sensations originate 

 either in the nerves, or the central medullary mass or brain ; 

 such are dreams, visions, and certain accidental sensations. 

 By central masses is to be understood, a part of the nervous 

 system, which is more circumscribed in the more perfect ani- 

 mals ; in man it is exclusively confined to a certain portion of 

 the brain, but in reptiles it consists of the brain, and all the 

 medullary matter of each part, taken separately, so that the 

 absence of the whole brain does not destroy sensation ; in the 

 lower classes of animals, the medullary mass is far more ex- 

 tended through the parts. 



The intellectual faculties possessed in a certain degree by 

 the superior animals are, perception, memory, the association 

 of ideas, imagination, volition, and reasoning. Our author 

 enumerates also the power of abstraction, but it may be doubted 

 whether abstraction can be effected without the aid of signs or 

 language. 



One privileged being, man, has the faculty of associating 

 general ideas with particular images, more or less arbitrary, 

 which are easily fixed in the memory, and which serve him to 

 recal the general ideas that they represent. These associated 

 images are what are called signs; collectively they form a 

 language. When language is composed of signs relative to 

 the sense of hearing, it is called speech. When the signs 

 relate to objects of sight, they are called hieroglyphics. Writ- 

 ing is a succession of images relative to the sense of sight, by 

 which we represent the elementary sounds ; and, in combining 

 them, we represent all the images relative to the sense of hear- 

 ing, of which speech is composed. Writing is, therefore, only 

 the mediate representation of ideas. 



This faculty of representing general ideas, by signs or 

 images that we associate with them, assists to keep them dis- 

 tinctly in the memory, and to recal an immense series of them 

 without confusion ; and furnishes to the reason and the imagin- 



