EXAMINATION OF BACTERIA WITH THE MICROSCOPE. 49 



methods for staining spores, but this procedure gives good 

 results. The principle is the same as in staining the tubercle 

 bacillus, except that more pains are needed to impregnate 

 spores with the dye. 



The spores are less readily stained than tubercle bacilli, and 

 for this reason require prolonged and repeated treatment with 

 the hot dye. The spores also give up the stain much more 

 readily than tubercle bacilli, and consequently will not retain 

 the stain if actively decolorized. Bacteria sometimes show 

 granules of protoplasm stained by the methods used for spores, 

 but these granules are not apt to be mistaken for spores. 



Staining of Capsules. — The capsules which many bacteria 

 possess appear to be made of gelatinous substance, which is 

 difficult to stain. 



Method of Welch. — {a) Cover-glass preparations are made 

 in the usual manner. Pour glacial acetic acid over the film. 



(b) After a few seconds, replace with aniline-water gentian- 

 violet, without washing in water. Change the stain several 

 times to remove all the acetic acid. Allow it to act three or 

 four minutes. 



(c) Wash and examine in salt solution, 0.8 to 2.0 per cent. 

 Bacteria are deeply stained, while their capsules are pale 



violet. This method has been recommended for staining the 

 capsule of the pneumococcus. 



Methods of Hiss.*— J. (a) Make cover-glass preparations in 

 the usual manner, and fix in the flame. 



(b) Stain for a few seconds in a half-saturated watery solution 

 of gentian-violet. 



(c) Wash in 0.25 per cent, solution of potassium carbonate in 



water. 



(d) Mount and study in the same. 



2. (a) Cover-glass preparations are made and fixed in the 

 ordinary way. 



^Journal of Experimental Medicine, VI., 1905, p. 317. 



