CHAPTER II 



OP CELLS AND OF NERVOUS FIBRES. 



All nervous system resolves itself under the microscope into cells 

 and fibres. All the nervous cords are almost exclusively com- 

 posed of fibres. On the other hand, the cells exist in very great 

 numbers in all the distended parts, in all 

 the central or ganglionary masses of the 

 diverse types of nervous systems. 



Though there are diverse varieties of cells 

 and of fibres, yet as the differences concern 

 only the details, it is possible to give of 

 them all a general description. 



The nervous cells are corpuscles of a 

 somewhat irregular form, and are more or 

 less spheroidal (Fig. 66). They liave a 

 wall, a content, a nucleus, and a nucleole. 



" * This last, of a brilliant and yellowish 



Fia. 66. 1 • • 1 1 1 



u. Bipolar nervouisoeu of the Colour, IS included in a large transparent 



ganglionof the trigeminoua j i -i i 1.1. jif* 



nerve of the trout, -with a ^'^u spnencai nucleus, which itself IS sur- 

 oontent.aTes'iouiSucieus rounded on all sides by a granulous and 



gangiiomJy°'cJu'"f°'ma^ solid' Substance. 



Usually a somewhat 



S^conSve'tosSe^^nl thick cellular membrane covers the whole. 



containing nnciei. According to M. Ch. Robin this mem- 



brane is lacking in the cells of the nervous centres of the 

 superior vertebrates. The diameter of the nervous cells varies 

 considerably. It is on an average from 0""°,020, to 0°"°,050. 



