446 A. B. MAOALLUM. 



obtained with it than to those of other histo-chemical reagents. 

 Gold chloride employed in any way is not an infallible test for 

 nerve-structures, for these have in the end to be determined by 

 their intrinsic form and arrangement, by their origin and 

 termination, or either separately. The violet colour given by 

 gold chloride to fibres otherwise undemonstrable is therefore of 

 accessory value only. 



It is not known definitely to what organic compound is due 

 the capacity of nerve-fibres for fixing in themselves gold chloride. 

 R. Gscheidlen,^ after a series of experiments, came to the 

 conclusion that the reduction is caused by a fatty substance. 

 He treated pieces of the ischiadic nerve of a frog with ether, 

 alcohol, and water respectively, and found that the extract 

 obtained with ether reduces gold in a few hours, while that 

 obtained with alcohol took longer to do the same, the aqueous 

 extract, on the other hand, a very long time. As 90 per cent, 

 of the solid extract obtained with ether is fatty in its nature 

 Gscheidlen drew the inference that a constituent of this fat 

 reduces the gold. I do not think that this explanation will 

 suffice, for nearly all the fat of such an extract must come from 

 the myeline investment of the fibres, and we find that no 

 reduction usually occurs in the medulla. FoP points out that 

 the violet colour may have another explanation than a mere 

 reduction of the gold, and calls attention to the fact demon- 

 strated by Lindet that this reagent forms double salts with 

 phosphorus compounds, especially the chlorides, which give 

 aqueous solutions of a violet colour. Whether gold chloride 

 undergoes reduction or enters into a more complicated condition 

 it is outside the province of the histologist to determine. It is 

 possible, however, without transgressing limits, to consider some 

 aspects of this question and to suggest some points which may 

 help in the solution It seems to me that the substance which 

 favours the production of a violet colour with gold chloride is 

 diffused through all forms of tissue, and that it is found in a 

 concentrated condition in nerve-tissue only. If a section of 



1 ' Arch, fiir Mikr. Anat./ Bd. xiv, p. 225. 



' ' Lehrbuch der Vergleichenden Microscopischen Anatomie,' p. 175. 



