106 THE MICROSCOPICAL NEWS. 
material we must still adhere to the tried and reliable methods of 
the past at the same time that we are reaching out by experiment 
to learn what is better, for it is only after the lapse of time that we 
are able to pronounce accurately in regard to the success of a par- 
ticular method. ; 
Among the new media, the solution of biniodide of mercury and 
iodide of potassium is one that is likely—on account of its high 
index of refraction (1.68)—to prove very useful for many purposes. 
Nevertheless, it will be found to act injuriously upon some struc- 
tures, and hence must be used with caution. It is undoubtedly 
superior to mono-bromide of napthaline forthe mounting of diatoms, 
besides being much more pleasant to manipulate, for the mono- 
bromide is certainly the most frightful combination of smells that 
the art of the chemist could concoct. Some experiments by Mr. 
E. E. Read, of the Camden Microscopical Society, would seem to 
indicate that cosmoline may prove a valuable medium in which to 
mount the starches. The starch grains are certainly remarkably 
well displayed in it. How permanent the mounts may prove is a 
question of time. It is not improbable that several of the petroleum 
products—even the plebeian kerosene itself—may be found not un- 
worthy of the microscopist’s attention. Many of the vegetable oils 
and balsams, too, will doubtless be found useful, as some of them 
possess high refractive indices and at the same time are good pre- 
servatives. Ouil of anise, according to Davis,* has a refractive index 
of 1.811, and the writer has used it to some extent with apparent 
success. Prof. Christopher Johnston has shown (Am. Monthly 
Mic. Journal, Oct., ’83) that balsam copaiba and damar is likely to 
prove a valuable medium. Dr. W. W. Munson some time ago 
called attention to the preservative properties of a solution of 
hydrate of chloral, and the medium is evidently deserving of more 
attention than it has had. A slide of algze put up in this solution 
over four years ago still remains as bright and pure as when first 
mounted, and, what is quite important, the cell contents of the algze 
appear to be less contracted than is usually the case. 
A compilation of the various formulas for mounting media which 
have been published from time to time would prove of great value, 
especially if accompanied by notes indicating the adaptation of 
each. 
Next to the choice of a medium, and of almost if not quite equal 
importance, is the choice of a suitable cell (if one is used), and a 
proper cement. It is absolutely essential in the case of both that 
they shall neither be dissolved nor acted upon chemically by the 
mounting medium. It may not be out of place here to mention 
an amusing personal experience, especially as it points a moral. 
* Practical Microscopy, p. 98. 
