io8 PRACTICAL' BACTERIOLOGY. 



these blood preparations^ since it has the power of 

 producing a greater contrast between the bacteria and 

 the various elements of animal tissue than any other 

 reagent. It may be used either in the aqueous or in 

 Loffler's solution. 



It is not advisable to apply heat whilst the process 

 of staining is going on, as, although the bacteria be- 

 come more quickly and intensely stained by this 

 means, the blood plasma, and especially the blood 

 corpuscles, are also much more coloured. If it should 

 happen that while the bacteria are well coloured, the 

 plasma and corpuscles are too deeply stained, the 

 preparation may be immersed for another moment in 

 1 per cent, acetic acid. Many bacteria are not in- 

 jured by remaining a somewhat longer time in weak 

 acetic acid, but others can only stand it for a second. 

 The cover- glasses, on being taken out of the acid, 

 are immediately plunged into water, in which they 

 are well shaken about, to remove the last trace of 

 the acid. 



Pus and the tissue-fluids, which are either squeezed 

 out of the organs,, or which during many infectious 

 illnesses collect in various parts of the body, should 

 be examined in a similar manner, in dry cover-glass 

 preparations. These substances are spread out upon 

 cover-glasses, fixed, treated with acetic acid, stained, 

 and eventually "^ difi"erentiated " again with acetic 

 acid. 



