ORDINARY STAINING-SOLUTIONS 173 



coagulated by the acetic acid is redissolved and rendered 

 invisible. This does not occur when the salt-solution is 

 of the proper strength — a point that can be determined only 

 after a few trials with solutions of different strengths. 

 (Welch.) A very clear, sharply cut picture usually follows 

 this method of procedure. 



Ribbert also recommends for the staining of capsulated 

 bacteria the momentary immersion of the cover-slips in 

 a saturated solution of dahlia in a mixture of 100 parts of 

 water, 50 parts of alcohol, and 12J parts of glacial acetic 

 acid; after which the excess of color is removed by washing 

 in water. 



Staining of Spores. — ^We have learned that one of the 

 points by which spores may be recognized is their refusal 

 to take up staining-substances when applied in the ordinary 

 way. They may, however, be stained by special methods; 

 of these, one that has given fairly satisfactory results in 

 our hands is as follows : the cover-slip is to be prepared from 

 the material containing the spores in the ordinary way, 

 dried, and fixed. It is then to be held by its edge with 

 forceps, and its surface covered with Loffler's alkaline 

 methylene-blue solution. It is then held over the Bunsen 

 flame until the fluid boils; it is then removed, and after a 

 few seconds is heated again. This is continued for about 

 one minute, after which it is washed in water and then 

 decolorized in 



Alcohol (80 per cent.) 98 c.c. 



Nitric acid . 2 c.c. 



until all visible blue color has disappeared. It is then rinsed 

 in water and dipped for from 3 to 5 seconds in 



Saturated alcoholic solution of eosin 10 c.c. 



Water 90 c.c. 



