THE MICROTOMIST 'S VADE-MECUM

In all cases wash out, before staining, with strong alcohol.    ,Suh
Nitric acid is penetrating, fixes well, and allows of good
staining. Some very delicate structures (cilia) appear to be      s
lost in the present mode of employing it. It will probably
came into much more general use.                                   Mo
28. Dilute Nitric Acid (Altmann's methods').-(Of general        ith lW'
histological application, but most specially referring      to    gj or
embryology.)                                                      Stii1 ch
Fixing.-IDilute nitric acid (containing from    3 to 31 per      r
cent. pure acid). Such a solution has a sp. gr. of about 1-02 ;
an areometer may conveniently be used to determine the            tur ds
concentration of the solution. Stronger solutions have been         R,1
used, but do not give such good final results.                     0
His2 recommended a 10 per cent. solution. Altmann tried
it, but found he could not demonstrate the nuclear figures.
He considers that the strong solutions coagulate the soluble
albuminoids of the tissues too strongly, which is a hindrance      s et
to the optical differentiation of structure. Flemming writes
to Altmann that he employs solutions of 40 to 50 per cent.           '
for the ova of invertebrates. This of course has the advantage
of a very rapid fixing action.                                      liat
The embryos, or other objects, are to be put fresh into the       ious
solution; it is useful, though not necessary, to employ a
liquid cooled to zero; the cold stops all molecular pro-
cesses, and the acid has time to fully complete the fixing           I
process.                                                            b
The objects must not be left too long in the liquid; for         chse
blastoderms and small embryos a quarter to half an hour is            n
enough, for larger ones two to four hours. Only small pieces         d
of tissues other than embryonic should be employed.
I understand the author to say that he then washes out
the acid, and completes the hardening in strong alcohol. He         Ai
points out that the process does not afford a true hardening         ithii
' Arch. Anat. u. Phys.,' 1881, p. 219.
2 ibid., 1877. p. 115.

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