STRUCTURE OF THE HUMAN BODY. 53 



spinal marrow, nerves and their ganglions/ The nervous tis- 

 sue appears to consist of two substances, which as far as the 

 eye can distinguish, appear to be entirely distinct from each 

 other. vThe one is called cineritious, or gray, from its col- 

 our ; from its position, cortical, and from its consistence pulpjrj 

 This last appears to be composed chiefly of blood-vessels. 

 The other is termed white, or medullary. It is of firmer 

 consistence than the pulpy. This is decidedly fibrous in its 

 nature. In every part of the nervous system which consti- 

 tutes a distinct nervous apparatus, both substances are con- 

 joined. Neither the pulpy, nor the fibrous alone, forms a 

 distinct organ ; the union of both is necessary to constitute 

 an instrument capable of performing a specific function. 



Ultimate fibres of nerve highly magnified ; showing the strings of 

 globules of which they consist. 



31. Much controversy exists in relation to the shape of 

 the ultimate particles of nervous matter ; but while micro- 

 scopical observations differ as much as they have done hith- 

 erto, the question may fairly be considered as unsettled, 

 ffhe common opinion is, that the ultimate filaments of which 

 they are composed, are formed of globules of extreme minute- 

 ness,) But then, when we consider the peculiar difficulties 

 attending investigations of this nature, that they require un- 

 wearied perseverance, extreme accuracy, great patience, and 

 a dexterity with the hand, united with a delicate discrimina- 

 tion of the eye, that belong to few ; and when we consider 

 moreover, that these very endowments can only be acquired 



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