76 STUDY AND IDENTIFICATION OF BACTERIA. 



parent when Gram's staining is used. This gives us great information, 

 as the diphtheria and the pseudodiphtheria are the only small Gram 

 positive bacilli usually found in the mouth. The cocci are also well 

 brought out. Neisser's stain gives a picture which, when satisfactory, is 

 almost absolutely characteristic. You have the bright blue dots lying 

 at either end of the light brownish-yellow rods. When first isolated 

 from a throat, the diphtheria bacillus is apt to stain characteristically by 

 Neisser. Later on, in subculture, there may be no staining of the 

 polar bodies. Neisser originally recommended five seconds' applica- 

 tion, with an intermediate washing, for each of his two solutions. 



FIG. 28. B. diphtheria stained by Neisser's method. (Williams.) 



Thirty seconds for each is probably preferable. Some authorities 

 recommend five to thirty minutes. It is well to bear in mind that 

 about 2% of the people in apparent health carry diphtheria bacilli in 

 their throats. 



Diphtheroid Bacilli. Pseudodiphtheria Bacillus. Hofman's 

 Bacillus. Under these terms various Gram positive bacilli have 

 been described as occuring in nose and in skin diseases: 



i. They very rarely give the blue dot staining at the two ends. 

 Exceptionally they may give a dot at one end. Neisser 



