METHODS OF OBSERVING BACTERIA. 99 



Spirillum of cholera and of chicken-cholera ; 

 Bacillus mallei (of glanders) ; 

 Bacillus of malignant edema ; 

 Bacillus pneumonise of Friedlander ; 

 Micrococctis gonorrhceae of Neisser ; 

 Spirochaete Obermeieri of relapsing fever ; 

 Bacillus of typhoid fever ; 

 Bacillus of rabbit-septicemia. 



Gram's method is a method of staining bacteria in 

 tissues, but the fact that the method colors some but not 

 all bacteria is one of considerable importance from a dif- 

 ferential point of view ; and as the difficulty of separating 

 the species of bacteria is so great that every such point 

 must be eagerly seized for assistance, this method be- 

 comes one much employed for cover-glass preparations, 

 where it is more easily performed than for sections. 



Gram's Method for Cover-glass Preparations. A 

 thin layer of the bacteria to be examined is spread upon 

 the cover-glass, dried, and fixed. The cover, held in the 

 grip of a cover-glass forceps, is flooded with Ehrlich's 

 solution. By holding the cover flooded with stain over 

 a small flame for a moment or two the solution is kept 

 warm, and the process of staining is continued from two 

 to five minutes. If the heating causes the stain to 

 evaporate, more of it must be dropped upon the glass, 

 so that it does not dry up and incrust. 



The stain is poured off, and the cover placed in a small 

 dish of Gram's solution and allowed to remain one-half 

 to two minutes, the solution being agitated. It is pos- 

 sible to apply the Gram solution in the same manner 

 in which the stain is used, but as a relatively larger 

 quantity should be employed, the dish seems preferable. 



The cover is next washed in 95 per cent, alcohol until 

 the blue color is wholly % or almost lost, after which it can 

 be counter-stained with eosin, Bismarck brown, vesuvin, 

 etc., washed, dried, and mounted in Canada balsam. 

 Given briefly, the method is : 



