126 Journal of Comfarative Neurology. 



(of potassium, sodium and ammonium, the first two in i ^ to 

 2%, the third in i^ % solutions), sulphuretted hydrogen (one 

 part of the saturated solution and three parts of distilled water). 

 One can also use with advantage the sulphocyanide (of potas- 

 sium, sodium and ammonium in 2% solutions). 



" The solutions of sulphite and hyposulphite, especially the 

 second, render necessary a careful watching of the preparations 

 that they are not entirely destroyed through a disappearance of 

 the metallic impregnation. 



"The sulphide (of potassium and sodium) are easier to 

 manage but the complete preservation of the preparations is not 

 entirely certain with them. 



" The sulphocyanide acts very well in bringing into view 

 the smallest parts upon which the metallic impregnation has act- 

 ed but it does not give a uniform black, only a brownish stain. 

 Besides this the cells and fibers under the action of this reagent 

 assume a punctate, almost pulverulent appearance. 



"Sulphuretted hydrogen is very disagreeable on account 

 of its offensive smell (a peculiarity which it has in common with 

 ammonium sulphide) and it also has a tendency (as has the am- 

 monium sulphide) to stain those parts containing no subli- 

 mate brownish, which impairs very greatly the clearness of the 

 preparation. 



" From all these grounds, and, particularly on account of 

 its rapidity and certainly of action, on account of the intensity, 

 uniformity and sharpness of the black stain obtained and on ac- 

 count of the certain permanency of the preparations, the mix- 

 ture used by photographers to stain and fix their pictures upon 

 aristotype paper is to be preferred to all the other substances 

 given here (naturally for the special purpose of the treatment of 

 the sublimate preparations). 



" From the many formulae of this kind which are found in 

 books on photographic technique, I have adopted one which I 

 repeat in a footnote.' 



'For toning the two following solutions are separately prepared : 

 (a) Water, i liter, 



Sodium hyposulphite, 175 g. 



