APPENDIX. 425 



i. Transfer to 95 per cent, alcohol 15 minutes. 



j. Dehydrate thoroughly in absolute alcohol 15 minutes. 



k. Clear sections in oil of turpentine 5 minutes. 



1. Mount in balsam as indicated above in 18. 



When hamatoxylin is used as the stain, the steps e, f, and g are 

 omitted and replaced by 



ee. Transfer to distilled water 5 minutes. 



ff. Stain in properly-diluted hsematoxylin fluid until sufficiently 

 dark 8-10 minutes. 



gg. Wash well in distilled water to remove excess of stain and to 

 differentiate 10 minutes ; then dehydrate by the ascending series of 

 alcohols included by h to j as above. 



The foregoing methods are those to be employed as the standard 

 processes, since for the great majority of specimens they yield results 

 perfectly satisfactory and trustworthy ; sometimes, however, special 

 lines of investigation demand other treatment in order to bring out 

 particular features. Several of those most important for the study 

 of the nervous system are here given. 



Weigert's hsematoxylin method is of great value in exhibiting 

 the presence and course of medullated nerve-fibres on account of the 

 peculiar staining of the medullary substance ; the method takes ad- 

 vantage of the tenacity with which this part of the nerve-fibre retains 

 the color, appearing slate-blue or black, while the other parts of the 

 nervous tissues become pale ; the tissue is first overstained and then 

 decolored. 



The fresh spinal cord or the brain is hardened in a large excess of 

 potassium bichromate (5 per cent, solution), repeatedly renewed, for 

 several weeks, and then directly transferred to 80 per cent, alcohol, 

 kept in the dark, and frequently changed uniil the fluid is no longer 

 discolored ; as the tissue is usually cut in celloidin, the next step is 

 the dehydration by 95 per cent, and absolute alcohol, followed by the 

 usual process of the celloidin embedding. After this has been ac- 

 complished, and the tissue is on the cork ready for cutting, the entire 

 block is transferred to 



a. Saturated solution neutral cupric acetate i part ; 



Solution of Rochelle salt ( 10 per cent.) i part, 



for 24 hours in oven at 40 C. 



b. Transfer to 



Saturated solution neutral cupric acetate i part ; 



Distilled water i part, 



for 24 hours. 



