48 TEXT-BOOK OF BACTERIOLOGY. 



Unfortunately, Gram's method is not equally applicable to all 

 micro-organisms. Typhus bacilli, the bacilli of Asiatic cholera, the 

 bacilli of the cholera of fowls, septicaemia of rabbits, and malignant 

 oedema, the bacteria found in pneumonia by Friedlander, the an- 

 thrax bacilli, the gonococci, and the spirilla of recurrent fever, can- 

 not absorb the color sufficiently to retain it; and under the influence 

 of iodine they lose color with the nuclei. For all the other bac- 

 teria, however, and especially for the great majority of the micro- 

 cocci yet discovered, this method has been found excellent. 



IV. PREPARATION OF COVER-GLASS SPECIMENS FOR 

 ST4INING. 



We now know what stains we can employ in the investigation 

 of bacteria, how they are prepared, how they may be varied, and 

 what the chief points are to be considered in the staining process. 



But to obtain fairly good results, it is indispensably necessary 

 to prepare the objects in a particular manner for the reception of 

 the stains. 



To do this take, with a bent wire previously heated in the man- 

 ner already described, a small portion of the liquid and spread it 

 in a very thin layer, as evenly as possible, over the cover-glass, or 

 remove a sample of the bacterial film from the surface of the boiled 

 potato, and with the aid of a drop of distilled water spread it over 

 the cover-glass. 



The preparation must be completely air-dried and the water 

 must be entirely removed. This process may be accelerated by 

 moving the cover-glass backward and forward at some distance 

 above a gas flame. Yet this must be done with the utmost caution, 

 lest the preparation should be overheated or even burned. It is 

 therefore best to hold the cover-glass between two fingers above 

 the Bunsen burner or spirit-lamp; the fingers are very sensitive 

 thermometers, and will be sure to give warning of any dangerous 

 proximity to the flame. 



Now allow the staining to proceed. As a rule, however, we have 

 not such exceedingly simple measures to deal with. The chief value 

 of staining is for cases in which the presence of bacteria is suspected 

 in the interior organism, and we must, therefore, examine blood, 

 tissue juices, pus, or sputum. Such preparations cannot be stained 

 immediately after they have been air-dried. 



They contain albumin, which is not rendered insoluble by simple 

 drying. When this albumin comes in contact with the dyes it 



