$28 General Notes. [ November, 
successful is shellac thoroughly incorporated with the finest car- 
bon (diamond black) such as is used in the preparation of the 
best printing inks; the solvent being alcohol, these rings dry 
rapidly, and the cover is attached by heating. Even these rings 
and which had been subjected for several hours to the heat of a 
steam bath. With large, somewhat coarse objects, the defect is not 
so marked, but with delicate ones, and especially test objects, it 
is simply a nuisance. With care I think the shellac rings may 
answer pretty well. I have not tried the aniline colored rings. 
The moisture (whatever it is) and the crystalline specks appear to 
be derived from the vaporizable parts of the wax or cement given 
off under conditions where one would suppose such a thing im- 
possible ; it is however a fact; I have the proof of it, and I dare 
say hundreds of others have, too plainly evident. There is 
another mode of making cells which promises well for perma- 
nence. My attention was first called to this method by Dr. Tulk, 
of London, who suggested for this purpose the thin gutta-percha 
tissue used by surgeons in the place of oiled silk. I have had 
special punches made which cut neat rings from this tissue, and 
I have used these rings with the greatest satisfaction. I have no 
preparation of my own more than two years old, these, so far, 
show no signs of change. Dr. Tulk informs me that he has them 
ten years old, and still good as when new. I have noticed that 
in some recent papers in the microscopical journals the writers 
who, with little experience, have so lauded wax rings, speak o 
“thin rubber” for rings. Evidently they have seen somewhere the 
gutta-percha mount, and supposed it rubber—the latter will not 
answer, melted rubber will not become hard. One beauty of the 
gutta-percha ring is the very moderate heat required ; it is thus 
available for many objects which might be injured by the greater 
heat necessary for the asphalt or shellac rings. As these rings, 
the arrangement of which I have spoken of, can be rapidly 
made, and as they can be kept for any length of time (shut away 
from the dust), they are at any moment ready as well as conve- 
nient for use. The preparation is first arranged, dried or burnt 
on the cover, the slide cleaned, a ring laid on the center, and on 
this the cover is placed; the whole is now held together by the 
forceps and slightly warmed, just sufficient to soften the gutta- 
percha ; the forceps may now be laid aside, or used simply to 
press the cover home, warming the slide gently, also the cover; 
the perfect contact of the softened “tissue” with the cover and 
slide is easily recognized, and with a little care this can be effected 
very quickly, and nothing further is necessary. A finishing nng 
of colored cement makes a very neat mount, but it is not neces- 
sary.—Prof. H. L. Smith, in “ Science.” 
