352 BACTERIOLOGY. 



from cases of suspected diphtheria they may lead to an 

 incorrect diagnosis. The Neisser staining method is of 

 value here, but, unfortunately, the absence of the stained 

 bodies is not a sufficient ground to exclude the possi- 

 bility of their being true diphtheria bacilli. There are 

 also some varieties which resemble the short pseudo- 

 bacilli in form and staining, but which produce acid in 

 glucose bouillon. These bacilli are found occasionally 

 in all countries where search has been made for them. 

 It may be added here that no facts have come to light 

 which indicate that bacilli which do not produce diph- 

 theria toxin in animals ever produce it in man. It 

 must also be borne in mind, however, that such proof 

 is necessarily very difficult to obtain. 



Mixed Infection in Diphtheria. Virulent diphtheria 

 bacilli, however, are not the only bacteria present in 

 human diphtheria. Various cocci, more particularly 

 streptococci, staphylococci, and pneumococci, are almost 

 always found associated with Loffler bacilli in diph- 

 theria, playing an important part in the disease and 

 leading often to serious complications (sepsis and bron- 

 chopneumonia). Indeed, the prognosis in a case of 

 diphtheria is now judged to be graver, other things 

 being equal, according to the degree in which other 

 pathogenic bacteria influence the course of the disease. 

 These cases of so-called mixed infection in diphtheria 

 have within recent years attracted considerable atten- 

 tion, and have been the subject of a number of animal 

 experiments. Though the results of these investiga- 

 tions so far have been somewhat indefinite, they would 

 seem to iudicate that when other bacteria are associated 

 with the diphtheria bacilli they mutually assist one 

 another in their attacks upon the mucous membrane, 



