iv GENEEAL PHYSIOLOGY OF NEEVOUS SYSTEM 177 



respectively, are composed. The physiological data we are about 

 to discuss will emphasise these differences. 



In reviewing our present knowledge of the minute structure of 

 the histological elements of the nervous system, it should be noted 

 that the data are all comparatively recent. Notwithstanding the 

 number and ability of the investigators and the delicacy and 

 variety of the methods employed, the facts are not yet sufficiently 

 clear and unequivocal to admit of the construction of any universal 

 and authoritative morphological theory. 



The first exact account of the existence of specific nerve-cells 

 dates from 1833, when Ehreuberg described the cells of the spinal 

 ganglia of the frog. In 1838 Eemak first discovered in the 

 sympathetic of vertebrates that the nerve-fibres are a prolongation 

 of the processes of the cells, which was confirmed in 1842 by 

 Helmholtz and Hannover on invertebrates. Deiters was the first 

 to demonstrate, in a monograph published after his death by 

 Schultze (1863), that two different kinds of processes can be 

 distinguished in the central nerve-cells nerve-fibres proper, and 

 protoplasmic processes. He proved the continuity of the former 

 with the axis-cylinders of medullated nerve-fibres, but left the 

 destination and physiological function of the latter undetermined. 



Gerlach in 1871, by the gold chloride method, demonstrated 

 the existence in the grey matter of the cerebrospinal axis of a 

 diffuse fibrillary network, which he interpreted as the result of 

 an anastomosis or concrescence of the finest ramifications of the 

 protoplasmic processes of the ganglion cells. To this he ascribed 

 the important function of bringing the ganglion cells of the central 

 mass of the nervous system into direct interrelation. 



In 1873 Golgi discovered his method of staining nerve-cells and 

 fibres black with salts of silver which led to a great advance in our 

 knowledge of the minute structure of the nervous system. He 

 showed that at a certain distance from the cells the nerve pro- 

 longations or axons give off collateral rami which branch from the 

 trunk, mostly at a right angle. Like Gerlach he admitted the 

 existence of a diffuse network of nerve-fibrils which conduct the 

 excitation ; but denied that it was formed by the dendritic 

 ramifications of the protoplasmic processes, which he held to be 

 simple nutrient paths from the cell body, with free endings. 

 Golgi maintained that the ganglion cells were united by a fibrillary 

 network formed of the finest ramifications of the axis-cylinders. 



Subsequent researches made by Eamon y Cajal after 1888, with 

 Golgi's methods, led this author to deny the existence of any such 

 diffuse fibrillary network : Cajal concluded that both the dendrites 

 and the axons terminate free ; and that each ganglion cell, with 

 the whole of its protoplasmic and axis-cylinder processes, represents 

 an elementary organism in itself, connected with the others not by 

 anastomosis nor continuity, but by simple contact or contiguity. 



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