772 The American Naturalist. [August, 
arranges them with a small brush. The slide is then carefully lowered 
into a dish of warm paraffine, and usually reaches the bottom without 
deranging the specimens. After cooling, the slide is taken out with 
the Con¥oluta still in place. From six to a dozen may thus be im- 
bedded and cut in a single series. 
Osmic Carmine for the Histology of the Nervous Sys- 
tem.—The gold chloride method serves only for the coarser anatomi- 
cal features of the nervous system. The finer structure can be studied 
to best advantage after treatment with osmic carmine. This new 
reagent is prepared as follows: Take a strong solution of carmine in 
ammoniacal water, and evaporate it on a water-bath until the appear- 
ance of red clouds on the surface indicates that the excess of: ammonia 
has disappeared. After cooling, add an equal volume of osmic acid 
(one per cent.), and filter under a bell-jar. A very dark fluid is thus 
obtained, which has the staining properties of carmine and the fixa- 
tive properties of osmic acid. At the end of some days this reagent 
loses its odor and becomes darker. Its fixative properties have disap- 
peared, leaving ita good macerating reagent. It is best, therefore, 
for preservative purposes to mix the acid and the carmine solution at 
the time of using, or at least not many days before. 
The Convoluta designed for sectioning ought to die extended. 
They will do this in a concentrated solution of sulphate of iron. As 
soon as they have been killed by this reagent they should be trans- 
ferred to the osmic carmine, and left from one-half to twelve or more 
hours, after which they may be hardened in the usual grades of alcohol 
or the examination of the ‘frontal organ’’ (olfacto-gustatory 
organ) in the living animal it was found necessary to resort to some 
immobilizing agent. Experiments with the various agents in common 
use showed that chlohydrate of cocaine (ten per cent.) was the best. 
A drop of a solution in distilled water was placed on a slide and 
evaporated slowly overa lamp. When the water had disappeared and 
- the slide had cooled a number of Convoluta were placed on the small 
spot of cocaine by the aid of a pipette, leaving as little water as pos- 
sible, so that they would be slightly compressed by the cover-glass. A 
good immersion lens was necessary, and examination had to be made 
with haste, as only two or three minutes elapsed before the tissue 
became opaque and began to change. 
