254 The Development of the Neuroglia 



plastic, nucleated mass in which the other elements of the nervous system 

 are embedded. The shape of a given portion of the mass (cell) depends 

 upon the shape of the space it occupies. The characteristic Deiters' cells 

 are to be observed only after the medullation of the axones has resulted 

 in interspaces giving them their shape. The pictures of Deiters' cells 

 obtained by the silver method (which, however, was not employed in 

 their original description) can be considered as the result of a deposit 

 usually beginning on the nucleus, clogging the mass about it, and ex- 

 tending variable distances along the filaments and trabeculge (processes) 

 connecting the mass with its neighbors. The earlier possibilities of such 

 appearances are shown in Fig. 12. This figure is taken from trans- 

 verse sections of the spinal cord of a foetal pig of 20 centimeters. The 

 processes of medullation are underway. The larger portion of the draw- 

 ing represents conditions shown by the Benda neuroglia stain and accom- 

 panying this are three masses chosen from a silver preparation of the 

 same specimen. Either of the masses designated by a can, -I think, be 

 correlated with silver picture a. The picture V can be looked upon as 

 a deposit of the silver upon a mass similar to that indicated by &. With 

 a little more clogging at the center this would give a neuroglia cell with- 

 out a nucleus. Masses similar to x can be easily imagined in the section. 



Many appearances to be observed in the pig are repeatedly described 

 in the literature employing the silver method. Also, for example, 

 Gierke, 85 and 86, who worked before the silver method was in general 

 use, described glia cells, nucleated and non-nucleated, and pictures them 

 with anastomosing processes. Some of his drawings are easily corre- 

 lated with the usual silver pictures. 



The size of a silver picture and the length and density of its processes 

 depend both upon the size of the mass and the extent of the precipita- 

 tion. The " processes " are seen to radiate in all directions, for the 

 reason that the sections in which they are seen are usually thick enough 

 to allow considerable perspective. Very long and finely attenuated pro- 

 cesses are more frequent after fibers are developed in the syncytium, 

 and many such processes no doubt represent fibers. 



The development of the neuroglia fibers from the syncytium is a pro- 

 cess of transformation. 



Fibers are first differentiated in the spinal cord of pigs from 16 to 20 

 centimeters. This is not till after the processes of medullation have 

 begun. Fibrillated areas and what appear as fibers occur in the syncy- 

 tium before this time, but by the Benda method they stain a light 

 brownish-red like the general sync3rtium instead of the deep blue charac- 

 teristic of neuroglia fibers. Therefore, by definition they cannot be con- 



