50 EXAMINATION AND STAINING OF BACTERIA. 



evenly upon it as few as possible of the bacteria to be exam- 

 ined. This is done by diluting with sterilized water a number 

 of times the culture containing them. The cover-glass is dried 

 and fixed in the ordinary way. The following solution, 

 known as a mordant, is then applied : 



Tannic acid (20 per cent, solution in 



water, filtered), 10 parts; 



Cold saturated solution of ferrous 



sulphate, filtered, 5 " ; 



. y Saturated alcoholic solution of fuchsin, 1 part. 



+ Ho 7.a Jrti OK tM.#&> v 



A few drops of it are placea on the film, and the cover-glass 

 taken up with a pair of forceps and held over the flame of a 

 Bunsen burner until the solution begins to steam, but not 

 allowing the boiling-point to be reached. It is next washed 

 rapidly in water, and then in absolute alcohol. The bacteria 

 are to be stained in anilin-water fuchsin solution in the ordi- 

 nary way. 



Practice has shown, however, that different bacteria behave 

 differently when exposed to this staining, and Loeffler himself 

 has modified it to meet these requirements. Having found 

 that the addition of an alkali favors the staining of flagella 

 in some of the bacteria, he has added to his stain 1 per cent. 

 of sodium hydrate. In other cases, having found that an acid 

 helps to bring out the flagella, he has added to his stain a 

 solution of sulphuric acid in water of such strength that 1 c.c. 

 will neutralize 1 c.c. of the sodium hydrate solution. 



The following bacteria require an acid solution added to the 

 stain : Bacillus pyocyaneus, the spirillum of Asiatic cholera, 

 Spirillum rubrum, Spirillum concentricum, Spirillum Metch- 

 nikowi. 



The following bacteria require an alkaline addition to the 

 staining solution : Bacillus mesentericus, Micrococcus agilis, 

 Bacillus typhosusj Bacillus subtilis, bacillus of malignant 

 oedema, Bacillus anthracis symptomatici. 



In a general way one may say that bacteria that produce acid 

 in the media in which they grow require the addition of an alkali 



