544 SUMMARY OF CURRENT RESEARCHES RELATING TO 



course to tlie silver nitrate. In this case, too, the pieces should 

 remain in the silver solution until wanted for immediate use, when 

 they are repeatedly soaked in frequently changed alcohol, passed 

 through absolute alcohol, creosote, oil of turpentine, to dammar. 



This last is the method most preferred by the author. 



In the method of the successive action of bichromate of potash 

 and of perchloride of mercury, the first stage is the same as that 

 which is given for the bichromate and silver methods. This over, the 

 pieces are placed in a • 5 per cent, solution of perchloride of mercury. 

 The reaction is effected in not less than eight days for small pieces, 

 while for large, such as whole brains, two months at least are 

 required. The perchloride solution must be renewed daily, until it 

 is no longer tinged with yellow. When the reaction has reached its 

 maximum, the nervous tissue is quite pale, and resembles fresh brain 

 matter recently washed in water. The pieces of nervous tissue may 

 be allowed to remain in the mercury solution for an indefinite period. 

 The sections may be mounted in some resinous medium, but in 

 either case frequent washing in water is necessary, in order to prevent 

 the formation of a deposit of acicular crystals upon the surface. The 

 sections are then dehydrated in alcohol, and having been cleared up 

 in oil of cloves or creosote, are mounted in dammar or in Canada 

 balsam. 



Application of Weigert's modified Hsematoxylin Stain to 

 the Peripheral Nervous System.* — Dr. T. Gelpke's experience 

 of the above method is that while it is most excellent in 

 principle, giving most brilliant results with normal nerves, yet, 

 when used to demonstrate certain morbid states, e. g. sclerosis, 

 the nerve-fibres were found to remain quite unstained, either 

 in longitudinal or in transverse section. By controlling experi- 

 ments made with osmic acid and carmine on sclerosed nerves, and 

 also by showing that the Weigert stain itself acted efficiently on 

 normal nerves, the author concluded that the want of success was to 

 be sought in the decoloration process. Further, that the ferrid- 

 cyanide solution was too strong, and as the result of his experiments, 

 he found that decoloration was most safely effected by using very 

 dilute solutions of the reagent. 



The author's emendation of this process is that for transverse 

 sections the ferridcyanide solution should be diluted down to one- 

 fiftieth of the strength given by Weigert. For longitudinal sections 

 a somewhat stronger solution may be employed. Naturally, the time 

 occupied by the stage is now much longer, decoloration taking from 

 one to twelve hours. 



Fixing Sections to the Slide.f— Mr. H. E. Summers says that 

 the following method has been tested with paraffin and celloidin 

 sections. For either kind of sections the slides are first coated with 

 collodion, either by flowing from a bottle or by a brush, and allowed 

 to dry. The celloidin used for imbedding, thinned with alcohol and 



* Zeitschr. f. Wise. Mikr.. ii. (1885) pp. 484-9. 

 t The Microscope, vi. (1886) pp. 66-7. 



