26 
SCIENCE. 
DRY “MOUNTS” FOR THE MICROSCOPE. 
BY PROFESSOR H. L. SMITH, HOBART COLLEGE, N. Y. 
What shall we use to preserve dry mounts effect, 
ually? Many may think that nothing is easier; a 
cell of Brunswick black ; a wax ring, or one of 
balsam ; but the question is not thus easily to be dis- 
posed of. The writer has, within the last five 
years, mounted, or has had mounted under his 
supervision, some 15,000 slides of various micros- 
copical objects, chiefly, however, foraminifera and 
diatoms ; half of these were dry mounts. 
Two things are important — the cell should be 
quickly and easily made, and the object when 
mounted in it should remain unchanged. There 
are very few cells as now made which will fulfil 
both these conditions, especially the latter. The 
deterioration of delicate dry mounts, and especially 
of test objects, sometimes within a few months after 
their preparation, but more or less certain in nearly 
every case, is well enough known. 
All of the dry mounts of the Eulenstein series of 
diatoms, e. g., which I have seen, are spoiled ; and 
my cabinet is full of such preparations. Even 
Moller’s do not escape, though they are, upon the 
whole, the most durable. I have abundance of 
amateur works that no doubt looked very beauti- 
ful just as they issued from the hands of the en- 
thusiastic preparers, which are now, alas, mere 
wrecks ; and worse than this, many choice and 
rare specimens, which I cannot replace, hopelessly 
ruined. 
I believe that I was the first one to suggest the 
use of sheet wax for the bottoms of cells for foram- 
inifera and other opaque objects, and of wax rings 
for diatoms and other transparent objects. (See 
Journal Quekett Club.) 
The number of spoiled specimens, especially of 
diatoms and delicate transparent objects which I can 
now show, proves that this method of mounting isde- 
cidedly bad. I have lived to see the day when I shall 
be quite glad if the responsibility of suggesting such 
a nuisance as the wax ring can be transferred to 
some one else. For large opaque objects like most 
of the foraminifera, seeds, pollens, &c., the object 
itself is not so much injured, but the covering glass 
will, sooner or later, become covered (inside the 
cell), on the under surface, with a dew like deposit, 
which, when illuminated, will glisten almost like 
so many minute points of quicksilver, and though out 
of focus when the object is viewed, will show very 
disagreeably, like a thin gauze between ; and with 
transparent objects these minute globules will not 
only dot the entire field, as so many dark or light 
points, but the object itself will appear as though 
it had been wetted. 
Not long ago a well-known optician showed to 
me a spoiled slide “ podura.” The scales were 
very good and large — in fact, it was a slide which 
I had given to him, and it had been selected by 
myself in Beck’s establishment in London as un- 
exceptionably fine. 1 his slide began slowly to show 
symptoms of “ sweating.” One scale after another 
appeared as though moisture had, in some mysteri- 
ous way, penetrated to the objects ; it was not water, 
however, for when the cover, after much trouble, 
had been removed, and warmed sufficiently 
to evaporate anything like water, the scales still 
exhibited the same appearance, and, in fact, the 
heat required to get rid of this apparent moisture 
was so great, that the scales were charred. When 
wax rings are used, this apparent wetting or 
“ sweating ” occurs quickly, and more disagreeable 
than this, innumerable elongated specks, possibly 
crystalline, appear all over the under surface of the 
cover-glass. The same trouble occurs when any of 
the ordinary asphalt preparations are used, and the 
only cement which 1 have thus far found to be toler- 
ably successful is shell-lac thoroughly incorporated 
with the finest carbon (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 cannot be trusted, unless thoroughly dry, and 
spontaneous drying is better than baking. 1 have 
had preparations spoiled after mounting on asphalt 
rings, which had been made for over a year, and 
which had been subjected for several hours to the 
heat of a steam bath. With large, somewhat course 
objects, the defect is not so marked, but with deli- 
cate ones, and especially test objects, it is simply a 
nuisance. With care I think the shell-lac rings may 
answer pretty well. I have not tried the aneline 
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 
tiling impossible ; 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 permanence. 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 inrepara- 
tions of my own more than about two years old ; 
these so far, show no signs of change. Dr. Tulk in- 
forms me that he has them ten years old, and still 
good as when new. I have noticed that in some re- 
cent papers in the mineralogical journals the 
writers, who with little experience, have so lauded 
wax rings, speak of “ thin rubber” for rings, evi- 
dently 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 neces- 
ary for the asphalt or shellac rings. As these rings in 
the arrangement which I have spoken of, can be rap- 
idly 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 convenient lor use. The 
preparation is first arranged, dried or burnt on the 
cover, the slide cleaned, a ring laid on the centre 
and on this the cover is placed ; the whole is now 
