134 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



one or many neurons. They are sometimes spoken of as inter- 

 mediate or association cells. 



Internal Structure of the Nerve Cell. Within the body of 

 the nerve cell itself the striking features of physiological signifi- 

 cance are, first, the arrangement of the neurofibrils, and, second, the 



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Fig. 63. Anterior horn cell fourteen days after section of the anterior root (Warring- 

 ton) : To show the change in the nucleus and the Nissl granules, beginning chromatolysis. 



presence of a material in the form of granules, rods, or masses 

 which stains readily with the basic anilin dyes, such as methylene 

 blue, thionin, or toluidin blue. This latter substance is spoken of 

 as the "chromophile substance," tigroid, or more frequently as 

 Nissl 's granules, after the histologist who first studied it success- 

 fully. These masses or granules are found in the dendrites as well 

 as in the cell, but are absent from the axon (see Fig. 62). Little is 

 known of their composition or significance, but their presence or ab- 

 sence is in many cases characteristic of the physiological condition 

 of the cell. After lesions or injuries of the neuron the material may 

 become dissolved and diffused through the cell or may decrease in 

 amount or disappear, and it seems probable, therefore, that it repre- 

 sents a store of nutritive material (Fig. 63). The non-staining 

 material of the cell, according to most recent observers, contains 

 neurofibrils which are continued out into the processes, dendrites as 

 well as axons. These fibrils may be regarded as the conducting 

 structure along which passes the nerve impulse. The arrangement 

 of these fibrils within the cell is not completely known, the results 

 obtained varying with the methods employed. A matter of far- 

 reaching importance on the physiological side is the question of 

 the existence of an extracellular nervous network. Most recent 

 histologists agree in the belief that there is a delicate network 

 surrounding the cells and their protoplasmic processes. This 

 pericellular net or Golgi's net is claimed by some to be a ner- 

 vous structure connecting with the neurofibrils inside the cell 

 and forming not only a bond of union between the neurons, but 



