with paraffin. Put the preparation on a hot stage already
warmed. As to temperature, Gaule cannot give absolute
directions, as the temperature of the preparations placed on
any form of hot stage is of course unknown; he can only
state that, using a Max Schultze's stage, the proper tempera-
ture was found to be attained when the thermometer stood
between 300 and 320 C.; he advises in no case to go beyond
320.  (The function of the quicksilver is, of course, to de-
fibrinate the blood by agitation. The concentration of the
NaC1 solution may be varied, though not beyond the limits
of from 0-3 to 3 per cent. It is important to remember that
the appearance of the Cytozoa is a periodical phenomenon.'
In November all frogs of over 50 grammes weight had Cytozoa,
whilst all frogs of less than 50 grammes were without them,
whilst in May frogs of under 50 grammes possessed them,
and those of over 50 grammes were without them. The
maximum of Cytozoa in large frogs is found in autumn, in
small frogs in spring. Gaule never found any in frogs under
20 grammes.)
The Cytozoa exist in quantities in liver, marrow of bone,
and spleen. They may be studied with the greatest ease by
simply teasing a piece of spleen with 0-6 per cent. salt-
solution, when they may at once be recognised in the spleen-
cells.2
Instead of 0-6 per cent. salt-solution it is sometimes useful
to employ a solution containing 0-3 per cent. chloride of
potassium, and 0-3 per cent. chloride of sodium.3
Good results are also obtained by adding to the 0-6 per
cent. salt-solution a trace of gentian-violet. After twelve to
twenty-four hours the blood-corpuscles will be found de-
coloured and stained, and may be treated with osmic acid and
dried for preservation.
1 Ibid., 1881 (Phys. Abtb.), p. 303.
2 2nd method, ibid., p. 307.
3 3rd method., ibid., p. 312.

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