218 
HENRY E. REBURN. 
toxylin, picro-carmine, gentian violet) after preliminary treat- 
ment with alcohol. Or if the dye is added first and the 
nuclei remain unstained, the stain in the nuclei becomes 
evident on subsequent addition of alcohol to the preparation. 
The difficulty of staining these nuclei in fresh preparations 
appears to have been noticed by others. Thus in Foster and 
Langley's ‘ Practical Physiology and Histology' (7tli edition, 
p. 125) I find this statement: “ The nuclei of the sheath 
may be stained by placing a piece of nerve after brief treat- 
ment with osmic acid in picro-carmine or haematoxylin for 
an hour." In Stirling's f Practical Histology' (2nd 
edition, p. 206) the directions for staining the nuclei include 
the statement that after osmic acid picro-carmine may be 
used, but it is best to leave them for several days in the 
stain. 
In consequence of these statements 1 made numerous 
preparations in order to see whether preliminary treatment 
with osmic acid will take the place of the alcohol, but with 
very indifferent results. Haematoxylin after osmic acid gave 
a brownish appearance to the whole nerve fibre, but the nuclei 
did not stand out ; and in the case of gentian violet after 
osmic acid the nuclei were apparent because they were 
stained less darkly than the rest of the fibre. Picro-carmine 
after osmic acid did stain the nuclei red, but this took a con- 
siderable time, and the preparations were not nearly so good 
as after treatment with alcohol. In A. B. Lee's ‘ Microtomists* 
Vade-mecum ' (7th edition, p. 136) I find the following, 
which seems germane to the present question : “ Living tissue 
elements in general do not stain at all, but resist the action of 
colouring reagents till they are killed by them. 
Objects which have been passed through alcohol generally 
stain better than those which have only been in watery fluids. 
But long preservation of tissues in alcohol is generally 
unfavourable to staining." 
It is well known that the nuclei of nerve fibres are usually 
quite well stained in sections, and in this case alcohol is 
usually employed in the stages of preservation or embedding. 
