1895.] Microscopy. 91 
To counteract the swelling effect of the weak solutions alcohol was 
employed. A 5 per cent. solution of formaldehyde in 50 per cent. alco- 
hol hardened pieces of earthworm and cat liver very rapidly, so that 
on the day following their immersion, sections could be obtained by the 
paraffin method. Here the nuclei were found not to have swollen 
noticeably, if at all, while nuclear detail was plainly brought out by 
staining. In the pieces asa whole, there was neither swelling nor 
shrinkage, while the liver did not become as pale as it would have in 
alcohol. 
For stains alum cochineal, Erlich-Biondi, Orth’s picro-carminate of 
lithium, Erlich’s acid hematoxylin, picric acid, fuchsin and saffranin 
were tried and their action found not to be very much if at all inter- 
ferred with by the formaldehyde. In oneinstance a piece of an earth- 
worm was placed in equal parts of 2 per cent. formaldehyde and alum 
cochineal. On the following day it had been little more than super- 
ficially reddened, while a piece that had been removed from the same 
solution (2 per cent.) of formaldehyde and left for the same length of* 
time in undiluted alum cochineal had stained perfectly. 
In Nostoc the dark yellowish-green has been extracted in 4 per cent 
formaldehyde leaving the filaments as seen with the naked eye of a 
whitish or very light green, while a dark green pond scum after 
immersion in the fluid for nearly two weeks has changed slightly to 
brownish-green. Still it is not unlike old specimens of the same and 
similar material that one often finds in ponds. 
In conclusion it may be said that for general purposes, solutions of 
at least more than 2 per cent. must be used in order to avoid the swell- 
ing and decolorization of specimens, that from 4-8 per cent. will give 
the best results. For histological purposes formalin combined with 
alcohol will give better results than either used alone; while the 
weak (1-2 per cent.) solutions by swelling nuclei may serve the very 
important special purpose of demonstrating the presence of cells not. 
otherwise readily distinguished. 
F. C. Kenyon. 
