XXxi\- JOUKNAI. OF COMPARATIVE Np:UKOLOGY. 



ing results obtained on using the method of Cox, presented by Bal- 

 i.ANCE and Stewart, in part at least, appear to reproduce artefacts, 

 since it is more than probable that certain of the processes of the 

 "spider cells," perhaps the greater number of them are in reality fibers 

 which are in close contiguity with the cells or nuclei, which are brought 

 to view by the precipitate and which are included in this precipitate 

 and thus made to appear as cell processes. A comparison may here 

 be drawn between spider cells (astrocytes) and the "spider cells" de- 

 scribed by Ballance and Stewart ; as concerns the former, evidence 

 is at hand which goes to show that certain of the processes of the astro- 

 cytes, as seen in Golgi preparations, are in reality neuroglia fibers 

 which are included in the precipitate which brings to view the cell 

 bodies of the astrocytes, such fibers thus presenting the appearance of 

 processes. Attention may further be drawn to the fact that these ob- 

 servers do not describe and show numerous newly formed medullary 

 sheaths or axis cylinders in relation with one neurilemma cell or nu- 

 cleus, as might be expected were the processes of the spider cells des- 

 tined to form new nerve fibers, unless it be assumed that only two of 

 the processes of a spider cell, arising from o])posite poles, are concerned 

 in the formation of a new nerve fiber. As previously stated, the use 

 of the term "spider cell" ris a means of designating the branched cells 

 seen in peripheral nerves, when stained by the Cox method, as is done 

 by Ballance and Stewart, is open to objection, unless it is their de- 

 sire to imply that these cells present the characteristics of the spider 

 cells (astrocytes) of the central nervous system, in which event it 

 should be recalled that astrocytes (spider cells of the central nervous 

 system — neuroglia cells) are not found in the peripheral nerves (excepting 

 optic and olfactory nerves). In their commentary on the regeneration 

 of axis cyhnders stained by the (tOloi method, Ballance and Stew- 

 art state that "it is clear, then, that the regeneration of axis cylinders 

 does not take place by a process of outgrowth from the proximal seg- 

 ment, but is commenced and completed by the activity of cells alreadv 

 existing in the trunk of the nerve. In the light of what has above been 

 said, it would seem permissible to make use of the Scotch verdict "not 

 proven." The observations of Bali.ance and Stewart pertaining to 

 the regeneration of the peripheral segment of a severed nerve, especiallv 

 those pertaining to the distal segment of severed but unsutured nerves, 

 are very important and are much more difficult to answer by observers 

 who adhere to the theory of the central origin of newly formed axis- 

 cylinders. Ballance and Stkwar r. as has been stated, find evidence 

 which leads them to sav that the new axis cvlinders and medullary 



