LABORATORY RESEARCH, ETC. 261 
Preparations.—Such precautions, and especially 
the most scrupulous cleanliness, are necessary in 
making preparations, since air, water, dust, the human 
hand, and instruments may all introduce foreign 
microbes. The instruments should be washed in abso- 
lute alcohol, and it is still more effectual to heat them 
to a temperature of from 150° to 200°. 
As to the ‘liquids (pus, mucus, etc.), the upper sur- 
face should not be taken, but that which is nearest to 
the tissues, and it should be spread on a thin slide 
by a platinum wire, which has been heated red hot 
and then allowed to cool. 
When the tissues are to be examined, part of them 
is detached by a knife which has been heated red hot. 
It is placed in Jung’s freezing microtome, in order to 
cut sections, after it has been hardened in alcohol, to 
which bichromate of potassium is sometimes added, 
The sections are made as large as possible, and are 
‘then instantly transferred to a capsule full of alcohol, 
in which they spontaneously unfold. The glass or 
platinum needle, and the nickel or platinum spatula, 
serve to spread out and smooth these sections. 
Staining Methods.—Aniline dyes have the property 
of giving a more vivid colour to the bacteria than to 
the surrounding tissues, often even without destroying 
them or altering their movements. This property has 
been turned to account, and the staining of preparations 
is now largely practised. - 
Methy!-violet, or fuchsin, in aqueous solution, serves 
