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. 



Methyl-violet, or fuchsin, in aqueous solution, serves 



