NEUROGLIA, AND SENSE ORGANS. 439 



5 per cent, of neutral acetate of copper, 5 per cent, of acetic 

 acid, and 2i per cent, of chronic alum, in water. Add the 

 alum to the water, raise to boiling point, and add the acetic 

 acid and the acetate, powdered (or [EwycL, 2nd ed., p. 303] 

 instead of the chrome alum, you may take chromium fluoride, 

 which obviates the necessity of boiling). If preferred, the 

 mordant may be dissolved in the formol solution, so that the 

 hardening and mordanting are done at the same time. 



After the mordanting the tissues are washed with water, 

 dehydrated, imbedded in celloidin, and sectioned. The 

 sections (not too thick) are treated for ten minutes with a 

 |- per cent, solution of permanganate of potash, and well 

 washed in water. They are then treated for two to four 

 hours with a solution of (l Chromogen." This is a naphthalin 

 compound prepared by the Hoechst dye manufactory. The 

 solution to be used is prepared as follows : 5 per cent, of 

 " Chromogen" and 5 per cent, of formic acid (of 1'20 sp. gr., 

 about four times as strong as the officinal) are dissolved in 

 water, and the solution carefully filtered. To 90 c.c. of the 

 filtrate are added 10 c.c. of 10 per cent, solution of sodium 

 sulphite. 



After this bath, the sections are put till next day into a 

 saturated (5 per cent.) solution of Chromogen. (Instead of 

 the Chromogen treatment, you may simply treat the sections 

 with PAL'S potassium sulphite, 783, and the results will be 

 nearly as good.) 



They are next carefully washed and stained. This is best 

 done oil the zlide. The stain is a warm-saturated solution 

 of methyl violet in alcohol of 70 to 80 per cent, (to which, 

 after cooling and decanting, there may be added, if desired, 

 5 per cent, of 5 per cent, aqueous solution of oxalic acid). 

 The sections are treated with this for a few seconds to one 

 minute, and mopped up with blotting-paper, then treated for 

 an instant with saturated solution of iodine in iodide of 

 potassium of 5 per cent. They are then differentiated till 

 clear and light blue with a mixture of anilin and xylol in 

 equal parts. Wash this out thoroughly with pure xylol, 

 and mount in balsam, or, preferably, turpentine colophonium. 

 Glia fibres and nuclei blue, cytoplasm invisible. 

 This method only gives good results with the human 

 subject. 



