THE MICROTOMIST'S VADE-MECUM

ligneous acid instantly kills Infusoria, Rhizopods, Daphnia,         t
Cyclops, Alga, &c., without altering their form. The acid          "inger
used is the Acetum pyrolignosum rectificatum. When it has          DOat
become turbid it must be filtered before being used.
The objects may be stained by means of anilin colours           tisue
dissolved in the acid.
Dissolve 1 part of anilin blue or diamond fuchsin in 200          43
parts distilled water; filter; and add 800 parts of pyro-
ligneous acid.                                                     nithost
The objects take some hours to stain. Apparently the             (fo I
author of this process mounts the objects in the solution with     ptame
which they were fixed !                                            Wi4e,
40. Acetic Acid. Formic Acid.-These two acids are useful        daI
and well-known fixatives of nuclei. Flemming, who has made         contain
a special investigation of their action, finds (' Zellsubstanz,'    1h
&c., p. 380) that the best strength is from  0-2 to 1 per cent.    Accord
Strengths of 5 per cent. and more bring out the nuclein            pieK
structures clearly at first, but after a time cause them    to     logical
swell and become pale, which is not the case with the weaker       they
strengths (ibid., p. 103).                                         nelei,
41. Alum.-Alum     has been used for fixing purposes, and        inn i
may therefore be mentioned here. Although quite super-              0nn1e6
seded for general work by other reagents, it may possibly          npi
still be found useful for certain special purposes.       For      lft
instance, for the preservation of Medusce the following process    and 1
has been recommended (by Pagenstecher).       Take two parts        Otail
of common salt and one of alum, and make a strong solution.         Arth
Throw the animals into it alive, and leave them      there for     ciliate
twenty-four to forty-eight hours. Preserve in weak alcohol.
A saturated solution of alum in sea-water preserves very well
the forms of Salpide, Meduse, Ctenophora, and other pelagic
animals. It constitutes a preservative medium in which the
objects may remain till wanted.
42. Iodine.-Iodine possesses considerable hardening pro-
perties, and a very high degree of penetration; and, in point

7) ~ nm~

36


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