246 PUBLIC HEALTH BACTERIOLOGY 

 DIPHTHERIA BACILLUS. 



Klebs first described the bacillus in the throat mem- 

 brane in 1883, and Loeffler first cultivated it in 1884 ; 

 hence called the Klebs-Loeffler bacillus. The toxins pro- 

 duced by it were investigated by Roux and Yersin in 1888- 

 89, and the antitoxins by Behring and Kitasato in 1890. 



Description. A slender bacillus, 1 to 6 micra long and 

 0-3 to i-i micron broad. From the throat they are mostly 

 4 to 5 micra long. They are rarely of uniform thickness 

 throughout, showing club-shaped thickening at one or both 

 ends. They are straight or slightly curved, stain deeply 

 with methylene-blue, often showing granules more darkly 

 stained, so that a dotted, beaded, or striped or barred 

 appearance results. The longer individuals often have 

 a strong resemblance to short chains of streptococci. In 

 18-hour-old cultures, many of the bacilli show on staining 

 deeply stained oval bodies situated most frequently at the 

 ends, the so-called " polar " or " Babes-Ernst " bodies. 

 These were first regarded as spores, but are now considered 

 to be chromatic granules. B. diphtheriae is an aerobe. Is 

 non-motile, non-sporing, non-flagellar, and non-liquefying 

 of gelatin. It is Gram-positive. 



Cultures. Grows on all media, but quickest and most 

 characteristically on Loeffler' s blood serum : [beef-blood 

 serum, 3 parts, 1 per cent glucose broth (meat infusion), 

 1 part. Put in tubes, slant, coagulate at 70 C, and 

 sterilize at 57 C. for 1 hour on eight days.] On this 

 medium colonies form in from 12 to 24 hours at 37 C, as 

 small circular discs of opaque whitish colour, like candle- 

 grease spots, and enlarging rapidly, outstrip any accom- 

 panying colonies of streptococci. 



On agar, a similar growth occurs, but less quickly, and 

 is closely resembled by that of Streptococcus pyogenes. 



In broth, a pellicle may form, and a turbidity which 

 however soon settles to the bottom, leaving the fluid clear 

 and producing a powdery deposit. 



It grows well in milk but does not clot it. 



Does not form indol. Ferments glucose, galactose, 

 laevulose, maltose, and glycerin, but not mannite or 

 saccharose. It reduces nitrate to nitrite. 



