BACILLUS DIPHTHERIA 567 



are poured into the tubes and the growth is gently emulsified in the 

 broth with a platinum loop. Two or three loopfuls of this emulsion 

 are then streaked over the surface of glucose agar, serum agar, or nutrose 

 agar. After twenty-four hours' incubation these plates show charac- 

 teristic colonies which can be easily fished and again transferred to 

 Loeffler tubes or any other suitable medium. 



Diagnosis. Cultures from suspected throats are taken on 

 Loeffler's blood serum medium and incubated at 37.5 C. for 12 to 18 

 hours. At the end of this time morphological examination by stain- 

 ing with Loeffler's alkalin methylene blue and by some polar body stain 

 like that of Neisser is carried out. Occasionally direct smears from the 

 throat may show the bacilli, but it is rarely possible to make a satis- 

 factory diagnosis in this way. 



Williams has pointed out that in throat cultures in which the diph- 

 theria bacilli are few in number it is of advantage to inoculate a tube of 

 ascitic broth with the mixed culture. The diphtheria bacilli will appear 

 in eighteen to twenty-four hours as a pellicle on the surface. A por- 

 tion of this pellicle may then be plated on ascitic agar and isolated in 

 pure culture from the colonies. This, however, is not necessary for 

 routine examinations. The important point is to take cultures as early 

 as possible on fresh and moist Loeffler's medium, avoiding the dried 

 tubes so often passed out from old stock at drug store stations. It is 

 important to smear from the actually involved areas, examining the 

 throat with good illumination, and to have the tubes incubated without 

 delay, instead of carrying them about for hours after inoculation. 

 Such cultures, examined by an experienced man should give positive 

 diagnoses in almost all of the actual cases. In the diagnosis of children 

 and in carrier work it is important to take nasal as well as throat cul- 

 tures. 



Pathogenicity. Bacillus diphtherias causes a more or less specific 

 local reaction in mucous membranes, which results in the formation of 

 the so-called " pseudo-membranes." When these are characteristically 

 present, infection with this bacillus should always be suspected. It 

 should be remembered, however, that membranous inflammation is not 

 necessarily present in all cases. We have seen positive cultures in a 

 considerable number of people, especially in relatively insusceptible 

 individuals, in whom the throat showed nothing more than severe con- 

 gestion and catarrhal inflammation. The consequent disease depends, 

 in part, upon the mechanical disturbance caused by the local inflamma- 

 tion and, in part, upon the systemic poisoning with the toxin which the 



