148 DIPHTHERIA AND PSEUDODIPHTHERIA. 



lar groups ; they may be straight or sometimes slightly 

 curved. Occasionally one or both of the extremities are 

 thicker than the rest of the body of the cell ; at other times 

 the centre of the cell bulges and the end of the cell tapers 

 (Figs. 56, 57, 58). 



Bacillus diphtherice stains with all of the anilin dyes and 

 by Gram's method, but better with Loeffler's alkaline meth- 

 ylene-blue solution. For the purpose of differentiation the 

 Neisser special stain is often used. 



The bacilli celts do not stain uniformly ; they contain large 

 granules, occasionally situated at one or both extremities or in 

 its central portion, which stain much more deeply than the rest 

 of the cells, and which make of a stained diphtheria prepara- 

 tion quite a characteristic picture under the microscope. 



Neisser's Differential Method. Some forms of false diph- 

 theria bacilli which can not be separated from diphtheria 



FIG. 58. 



Diphtheria bacilli characteristic in shape but showing even staining. In appear- 

 ance similar to the xerosis bacillus. X 1100. Stain, inethylene-blue. 



bacilli by their mode of growth or by their appearance under 

 the microscope, but which are not toxic, must be differen- 

 tiated from the toxin-producing bacilli ; and Neisser has 

 suggested the following method, which is used in a number 

 of municipal laboratories. It consists of two solutions, as 

 follows : 



