BACTERIA PATHOGENIC TO MAN 



onds, and then, after washing, in No. 2 for from three to five seconds. 

 The bacilli will then appear either entirely brown or will show at one 

 or both ends a dark-blue, round body. With characteristic diphtheria 

 bacilli, taken from a twelve to eighteen hours' growth on serum, nearly 

 all will show the blue bodies (Fig. 76), while with the pseudotype (Fig. 

 83, page 197), to be described hereafter, few will be seen. 

 The solutions are as follows: 



No. 1. 



Alcohol (96 per cent. ) 20 parts. 



Met hylene blue (Griibler) 1 part. 



Distilled water 950 parts. 



Acetic acid (glacial) 50 " 



No. 2. 



Bismarck brown ...... 1 part. 



Boiling distilled water ..... 500 parts. 



The Neisser stain has been advocated in order to separate the viru- 

 lent from the non-virulent bacilli, without the delay of inoculating 

 animals; but in our hands, with a very large experience, neither the 

 Neisser stain nor other stains, such as the modifications of the Roux 

 stain, have given much more information as to the virulence of the 

 bacilli than the usual methylene-blue solution of Loeffler. A small 

 percentage of virulent bacilli fail to take the Neisser stain, and quite a 

 few non-virulent pseudodiphtheria bacilli show the dark bodies. In 

 New York there are also a large number of bacilli which seem to have 

 all the staining and cultural characteristics of the virulent bacilli, and 

 yet are non-virulent in the sense that they produce no specific toxin. 

 To one who is accustomed to the Loeffler stain it gives as much informa- 

 tion as any other, as to the specific virulence of the bacilli. The Neisser 

 stain as well as some others will undoubtedly cause the examiner to 

 suspect more strongly some bacilli of being virulent than the Loeffler 

 stain, but with the varieties met with in New York this suspicion is as 

 apt to be wrong as right. As will be stated more fully later, nothing 

 but animal inoculations with control injections of antitoxin will separate 

 bacilli capable of producing diphtheria toxin from others. 



The morphology of the diphtheria bacillus varies considerably with 

 different culture media employed. On glycerin agar or simple nutrient 

 agar there are two distinct types. One grows as smaller and, as a rule, 

 more regular forms than when grown on serum culture media (Fig. 78). 

 The other type shows many thick, Indian-clubbed forms with a moderate 

 number of segments. Short, spindle, lancet, or club-shaped forms, 

 staining uniformly, are all observed. The bacilli which have developed 

 in the pseudomembranes or exudate in cases of diphtheria resemble in 

 shape young bacilli grown on blood serum, but stain more evenly. 



Biology. The Klebs-Loeffler bacillus is non-motile and non-lique- 

 fying. It is aerobic. It grows most readily in the presence of oxygen, 



