Obersteiner, The Structure of the Nervous System. 77 



they are easily made visible by a new method (Kronthal, Neurol, 

 centralbl., 1890). In the cells they suffer a certain change of 

 position and pass out by way of other processes. These prim- 

 itive fibrillae are thus the essential conducting elements. Very 

 different, however, is Nansen's conception (Anat. Anz. , 1888). 

 He considers that the axis- cylinder consists of a great number 

 of closely arranged primitive tubes. These are composed of 

 exceedingly fine connective tissue sheaths (spongioplasm) with 

 viscous contents (hyaloplasnji). The compressed cells of the 

 walls between the primitive tubes were mistaken for primitive 

 fibrillae. It is not, therefore, the latter which are to be regarded 

 as the physiologically important elements of the axis-cylinder, 

 but those parts which were before taken to be a fluid intermedi- 

 ate substance. This tubular structure, in accordance with Nan- 

 sen's views, appear also to the bodies of nerve cells. 



Every nerve cell possesses at least one process ; but such 

 unipolar cells are exceptional and we have concerned ourselves 

 with those cells only from which several processes may be ob- 

 served. 



As is well known, Deiters (1865) first suggested that all 

 central ganglion cells have two distinct kinds of processes : an 

 axis cylinder process and a variable number of protoplasmic pro- 

 cesses. With reference to the first, Deiters had previously 

 maintained that it posses directly into a (medullated) nerve fibre. 

 This opinion has been shared by almost all investigators until 

 now, and apparently properly so. Really, however, such an 

 indubitable passage into the nerve has hitherto been observed 

 only a few times (e. g. Koschewnikoff, Freud); and even if the 

 axis-cylinder process, chief process, or nerve process can be dif- 

 ferentiated from the protoplasmic processes by the appearance 

 which it presents, especially after treatment with Golgi's impreg- 

 nation with silver, still the conscientious investigator will be in 

 doubt to which of the processes he should give the precedence 

 in the case of very many cells observed under the microscope — 

 nay, rather, in the case of most of them. I do not then con- 

 sider quite just and candid the reproduction, in many illustrations, 

 of nerve cells strictly true to nature, even to the color (black) 

 produced by silver impr.egnation, while those processes only 



