405 
Rhabdonia tenera , J. Ag. 
the gelatine was then removed from the exterior by washing 
in warm water, and the object was placed on the freezing 
chamber in a gum-arabic solution and cut. Most excellent 
results were obtained by this method, and all delicate parts 
were held in place. The sections were removed from the 
knife, placed in a watch-glass in 20 °/ o glycerine, which was 
allowed to stand until it became considerably more concen- 
trated ; enough 50 °/ o gelatine was then added over a water- 
bath to make a good glycerine-jelly, and the sections were 
placed on a slide in a drop of this and mounted. The whole 
process can be carried out on the slide, but it is much easier 
to treat a great many sections at once in a watch-glass. If it 
is not desirable to mount them at once, it is only necessary 
to protect the glycerine-jelly from evaporation, and it can be 
kept indefinitely. In many cases it was found convenient 
to prepare thick sections in this way, and mount them 
between two covers so that they could be studied from 
both sides. If it is desirable to fix such a preparation per- 
manently to the slide, Canada-balsam makes a sufficiently 
good cement. 
Sections made from material not previously infiltrated with 
gelatine were mounted in glycerine-jelly or glycerine. In 
the latter case it was found advantageous to mount in 20 °/ o 
glycerine, and after the latter had become more concen- 
trated by standing, to ring the preparation with a syrupy 
solution of gum-arabic. This forms around the edge of 
the cover a glycerine-gum which becomes hard in a short 
time, and the preparation may then be ringed with Canada- 
balsam. 
Numerous stains were tried, of which Heidenhain’s iron- 
alum haematoxylin proved to be by far the best. Anilin 
stains and the ordinary haematoxylin mixtures have the 
disadvantage that they stain the gelatinous wall and inter- 
cellular substance deeply. On the other hand a purely 
aqueous haematoxylin and Schneider’s aceto-carmin are free 
from this objection, but they stain all protoplasmic structures 
rather diffusely. With Heidenhain’s method the gelatinous 
