40 Joi^KNAL OF Co.Ml'AKATINE NEUlU)LO(iY. 



Professor Herrick, I have been enabled to consult the greater 

 part of the recent and a number of the older works upon 

 this subject. In this connection, I thank Prof. Herrick, not 

 only for the use of his library, but also for many valuable 

 suggestions. 



Technique. — Almost all of the brains examined were 

 hardened in dilute chrom-acetic acid and alcohol. A solution 

 of chrom-acetic acid of from one-third to one-half of the 

 ordinary strength was found to be the most useful. The 

 fresh brain was placed in this fluid and allowed to remain 

 for twelve hours. It was then thoroughly washed with 

 distilled water and hardened in increasing strengths of 

 alcohol. After a specimen had been in 90 per cent, alcohol 

 for a short time, measurements were taken and its external 

 appearance was recorded. 



Staining. — In preparing specimens for histological study, 

 several stains were tried. In a few cases, Kleinenberg's 

 haematoxylin gave good results: in others, it was a failure. 

 Grenadier's ha^matoxylin, applied to sections, sometimes 

 gave good results. 



The best results, however, were obtained from aluminium 

 sulphate cochineal.(') In using this stain, the specimens 

 were transferred from 90 per cent, alcohol to 70 per cent. 

 After remaining for one day in this grade of alcohol they 

 were transferred to the stain and allowed to remain in it for 

 three or four days. They were then thoroughly washed in 

 70 per cent, alcohol, after which they were hardened and 

 sectioned in the usual way. 



When the brains are prepared in this manner, the neu- 

 roglia does not stain at all, while the nerve cells are stained 

 and their nuclei and nucleoli well diflerentiated. The red 

 blood-corpscules also stain, but they stain much more densely 

 than the nerve cells. Fibres do not stain, Init, in most cases, 

 can be readilv traced. 



t This stain is jjreparcd by sul)';tir\iting aluminium sulph.ati: for the alum in Czokor's 

 alum cochineal. 



