ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
589 
The imbedded pieces are then immersed for 12-24 hours in a mixture 
of spirit and nitric acid (15-40 parts HN0 3 sp. gr. 1*4 and 100 parts of 
alcohol 85 per cent.). Each piece requires at least 20 ccm. of the fluid. 
The pieces are next transferred to 85 per cent, alcohol which contains 
some precipitated carbonate of lime, until every trace of acid is removed. 
They are then placed in 85 per cent, spirit, and sections made. 
For desilication, sponges are treated with fluoric acid, after pieces 
have been imbedded in celloidin as in the previous method. Of course, 
all the vessels and instruments used must be made of, or covered with 
caoutchouc or paraffin. A piece of sponge imbedded in celloidin is 
placed in a caoutchouc capsule, having a lid, and containing at least 
50 ccm. of alcohol. To this commercial hydrofluoric acid is added drop 
by drop up to 20 or 30 drops, according to the amount of silica in the 
sponge. The desilication takes from one to two days. The pieces are 
then placed in 85 per cent, alcohol containing some lithium carbonate. 
If there be any precipitate in the tissue, it may be subsequently removed 
with hydrochloric acid alcohol. 
By this procedure very good sections of TetJiyx, Suberites, Thenia , 
Geodia, Beniera , &c. can he obtained. 
(3) Cutting, including Imbedding and Microtomes. 
Improved Cathcart Microtome.* — Herr C. Elbe describes slight 
improvements in the Cathcart microtome (fig. 52). To prevent slipping 
* Zeitschr. f. angew. Mikr., iii. (1897) pp. 147-9 (1 fig.). 
