190 



PHYSIOLOGY 



CHAP. 



demonstrated the fusion of the axis - cylinder fibrils into an 

 intracellular elementary network, that the nervous system is 

 constructed of ganglion cells and of a fibrillary nerve substance, 

 the latter being a specifically differentiated cell protoplasm, 

 present in the cells as fibrils, and outside them as grey matter, 

 which last apparently consists of a close and very delicate 

 network of elementary fibrils. So that Nissl, like Bethe, considers 

 the grey matter to be the most important constituent of the 

 nervous system. 



Another method, which brings out the fibrillary character of 

 the nerve-cells, is that discovered by Eamon y Cajal ; it depends 

 on the reduction of silver nitrate, and is known as the photo- 

 graphic method. According to Golgi the results obtained by 

 it are of the utmost importance and are easy of demonstration. 



FIG. 125. Three nerve-cells and processes showing presence and course of neuro- fibrils. ' 

 Ramon y Cajal's photographic method. 



Cajal's method (Fig. 125) shows up every detail, so that the 

 course of the fibrils can be followed both within the cell body 

 and in the processes. Among its other advantages is the fact 

 that, unlike any that preceded it, it brings out the fibrillary 

 structure of the nerve elements during their earliest development. 

 Jaederholm, nevertheless, remarks with regard to the signifi- 

 cance and theoretical value of these histological observations : 

 " In my opinion the reticular formations within the cells must 

 be regarded as artificial products due to agglutination. Such a 

 reticular formation may be simulated, because the cytoplasm, 

 coagulated in the form of a network, stains along with the 

 fibrils ; this happens most frequently with Donaggio's method ; 



