308           THE MICROTOMIST' S VADE-MECUM
The best fixing agent in general is the chromo-aceto-osmic iaR
acid mixture (No. 14). Attempts to omit the chromic acid        utkct
did not give good results. The omission of acetic acid (as in   ad
Max Flesch's formula, No. 13) causes the figures to be far      gtn ai8
less sharply brought out. The presence of acetic or formic      $stain
acid in all osmium  solutions is favorable to the precision of  giie
subsequent staining with hnematoxylin, picro-carmine, or         ailes
gentian-violet. But mixtures of osmic and acetic acid with- 5he
out chromic acid (Eimer) do not give such good results as naphth
the chromo-aceto-osmic acid mixture. Mixtures of picric 6olh
acid with osmic acid or with osmic and acetic acid (propor-      es
tions of the latter as in the chromo-acetic osmic mixture (14), Rbt a
but of picric acid about 50 per cent.) fix quite as well as the  ldan
chromic mixtures, but precise staining is even more difficult    087
than with pure osmic-acid preparations. Flemming concludes      ad
that the beneficial effects of the osmium in all these mixtures  Enida
are to be ascribed to the instantaneous rapidity with which it  wet
kills, the function of the other acids of the mixture being to  (Klein
render the structures distinctly visible.                       lhi
Mixtures containing osmic acid should therefore be em-        naneRI
ployed whenever it is desired to fix the chromatic figures as   mania
faithfully as possible; whilst pure chromic acid should be      acoin
taken whenever very sharp staining is the more important         specin
point.                                                           insist;
For the study of the achromatic figures he recommends the     usen
chromo-acetic acid mixture No. 15, followed by staining in      tol0
heematoxylin (anilins do not give so good results for this      obtain
purpose).                                                       Ce
For the study of polar corpuscles he recommends the           hm;
osmium mixtures, or pure chromic acid followed by staining       E,
with gentian-violet. tlt
For pure nuclear stains he continues to prefer the Battcher-   t
Hermann method (No. 136). The stains recommended most anill
are safranin, rose de naphthalin, dahlia, and gentian-violet. tin pa
For fresh preparations mixtures of methyl-green and acetic