656 Wisconsin Academy of Sciences, Arts, and Letters. 
side while the other is being wiped. The cover glass and slide 
are next carefully cleaned with a camel’s-hair brush moistened 
in alcohol to remove all traces of glycerin. The mount may now 
be finally sealed in the usual manner; about six coats of cement 
should be used, and each one should be allowed to dry thoroughly 
before applying the next. The first coat should always be an 
alcoholic cement, as this will absorb any small quantity of glycerin 
present and the covers will stick much better. 
If the transfer to glycerin can not be accomplished and the 
animals persist in shrinking, they should be mounted in 2 per 
cent, formalin in hollow ground slides. It is extremely doubt¬ 
ful whether really permanent mounts in a watery medium can 
be made; no cement is known that is absolutely impermeable to 
water. A slide made according to the following method, originated 
by Rousselet, will last 5 or 10 years, seldom longer. A ring of 
benzol lammar, about 1 part dammar in 15 parts benzol, should 
be spun on the slide, about 1 millimeter outsile the edge of the 
cavity; this ring must be very thin, or the rotifers will get be¬ 
tween the cover and the flat top of the slide, and as evaporation 
proceeds they will become crushed. The first ring of cemeuf 
should be made with Windsor and Newton’s “Picture Copal 
Varnish”, and this should be followed by 5 or 6 coats of gold size. 
If a small air bubble is included in the cell at the time of mount¬ 
ing, the slide will probably last much longer, as this allows the 
liquid to expand and contract without straining the cement ring. 
All slides mounted with watery media or glycerin should be 
stored lying flat, or the specimens will gradually work down to 
the edge of the cell and either be caught in the cement, from 
which they are removed only with great difficulty, or get under 
the cement ring on top of the cover and thus become invisible. 
