THE MICROSCOPE AND MICROSCOPIC METHODS 51 



is removed from everything except the spores by the acid alcohol. 

 The methylene-blue solution stains the bodies of the bacteria, 

 the spores remaining brilliant red. There are various other 

 methods for staining spores, but this procedure usually 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. 



When it fails, the cover-glass preparation may be treated by 

 Moeller's method previous to staining. After fixation, the prep- 

 aration is immersed in chloroform for 2 minutes, drained and 

 dried in the air. It is then immersed in 5 per cent chromic 

 acid for 2 minutes, washed thoroughly in water, and stained 

 as above described. 



Staining of Capsules. The capsules which many bacteria 

 possess, appear to be made of some 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. 



(&) 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 sa,lt 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. i. (a) Cover-glass preparations are made 

 in the usual manner, and fixed in the flame. 



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

 tion of gentian violet. 



(c) Wash in 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. 



