XXXl] SPINAL CORD 247 



They are perhaps best imbedded in celloidin, but they may 

 be imbedded in paraffin ; to prevent the xylol or other clearing 

 agent dissolving the osmic acid stained medulla it is advisable 

 after treatment with osmic acid to keep the pieces for some 

 time in alcohol. 



The method may be modified in the following way : the tissue 

 hardened in Miiller's fluid or potassium bichromate is soaked in 

 the same fluid saturated with gum, then cut frozen, and the 

 sections placed in the chromic-osmic mixture. Some of the 

 sections may be stained with picrocarmine. 



GolgVs chromate of silver method. See p. 240. The mixture 

 consists of 1 vol. of 1 p.c. osmic acid, and 4 vols. of 3 p.c. 

 potassium bichromate. 



In order to obtain successful preparations it is generally 

 necessary to place a number of pieces in the osmic-bichromate 

 mixture, and to transfer them to silver on successive days. After 

 a day in the silver, a section is prepared from each free-hand, if the 

 preparations are not successful they are passed once more through 

 the fluids. Some pieces may also be left 2 or 3 days in the 

 nitrate of silver instead of 1 day, but as a rule repeating 

 the treatment with the fluids is more successful. 



According to Lenhossek, 2 or 3 days in the osmic-bichromate 

 mixture is best for neuroglia cells, 3 to 5 days for nerve -cells, and 

 5 to 7 days*for nerve fibres. 



Neuroglia stain. (Weigert ; for human nervous system.) 

 Small pieces of the spinal cord are placed for 8 days or longer in 

 the chrome alum and acetate of copper mixture (p. 301), they 

 are then washed, imbedded in celloidin and cut. 



The following solutions are required : 



(1) '25 p.c. potassium permanganate. 



(2) (a) 5 grams chromogen. 



5 c.c. formic acid. 



60 c.c. water. 



The solution is filtered. 



(6) 10 p.c. sodium sulphite. 



