BY J. T. WILSOX AND C. .J. MARTIN. 667 



of our own photomicrographs. "If," he says, "they estabhsh 

 nothing else, they certainly prove that this conclusion as to the 

 nature of the filaments [that they are nervous in character] is 

 erroneous; neither naked axis-cylinders nor nerve fibrils could 

 have caused the appearances seen in transverse section in PI. xxv. 

 fig. 13, and in longitudinal section in fig. 8." And why not? 

 Apparently merely because we have clear and unstained dots and 

 lines in two (bi-chromate) preparations stained respectively with 

 anilin blue-black and haematoxylin, reagents which in tissues 

 hanlened with clnximic salts are not to be depended upon as axis- 

 cylinder stains. What, we must ask, are the histological criteria 

 of nerve-fibrils and axis-cylinders'? The absolute test of the 

 nervous character is of course the histogenetic one. If these 

 filaments are, morphologically, outgrowths or prolongations of 

 axis-cylinders (which in turn are simply the processes of nerve- 

 cells), then we presume that no slight histological modification of 

 the ultimate ramifications of such a process would prevent us 

 from assigning to them a distinctly nervous character. This we 

 premise because we believe that these terminations of axis- 

 cylinders (as we confidently regard them) have undergone some 

 very slight histological or chemical modification. But it is of the 

 utmost importance to note that whatever change may have 

 occurred has been far too slight to affect those fundamental 

 micro-chemical reactions to certain stains which, in the absence 

 of the histogenetic test, constitute our ultimate criterion of their 

 nervous character. 



It was upon the strength of the argument derived- from the 

 reaction to gold salts that in (»ur former paper we confidently 

 pronounced these filaments to be nervous, nor should we now see 

 any valid reason for rejecting that conclusion even if no fui-ther 

 facts were before us. 



It seems appropriate here to notice a curious little mistake 

 Professor Poulton appears to make in i-eference to the gold 

 reaction upon the fibrils. After admitting the conclusiveness of 

 our gold-stained preparations as to the continuity of the fibrils 

 with the axis-cylinders at the base of the rods, he goes on to say: 



