198 BACTERIA PATHOGENIC TO MAN 



antly than the diphtheria bacilli. Some of the varieties of the pseudo- 

 diphtheria bacilli are as long as the shorter forms of the virulent bacilli. 

 When these are found in cultures 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 

 in smears of mixed cultures is not a sufficient ground to exclude the 

 possibility of their being true diphtheria bacilli. There are also some 

 varieties which resemble the short pseudobacilli 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 diphtheria toxin in animals ever pro- 

 duce 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 

 also found associated with Loeffler's bacilli in diphtheria, playing an 

 important part in the disease and leading often to serious complications 

 (sepsis and bronchopneumonia). Indeed, the prognosis in a case of 

 diphtheria is now judged to be graver, other things being equal, accord- 

 ing to the degree to which other pathogenic bacteria influence the 

 course of the disease. These cases of so-called mixed infection in diph- 

 theria have within recent years attracted considerable attention, and 

 have been the subject of a number of animal experiments. Though 

 the results of these investigations so far have been somewhat indefinite, 

 they would seem to indicate that when other bacteria are associated 

 with the diphtheria bacilli they mutually assist one another in their 

 attacks upon the mucous membrane, the streptococcus being particu- 

 larly active in this respect, often opening the way for the invasion of 

 the Loeffler bacillus into the deeper tissues or supplying needed condi- 

 tions for the development of its toxin. Thus diphtheria is not always 

 a primary, but often a secondary disease, following some other infec- 

 tion, as measles or scarlet fever. In most fatal cases of bronchopneu- 

 monia following laryngeal diphtheria we find not only abundant pneu- 

 mococci or streptococci in the inflamed lung areas, but also in the blood 

 and tissues of the organs. As these septic infections due to the pyo- 

 genic cocci are in no way influenced by the diphtheria antitoxin, they 

 frequently are the cause of the fatal termination. Other bacteria cause 

 putrefactive changes in the exudate, producing alterations in color 

 and offensive odors. 



Pseudomembranous Exudative Inflammations Due to Bacteria other 

 than the Diphtheria Bacilli. The diphtheria bacillus, though the most 

 usual, is not the only micro-organism that is capable of producing 

 pseudomembranous inflammations. There are numerous bacteria 

 present almost constantly in the throat secretions, which, under cer- 

 tain conditions, can cause local lesions very similar to those in the less- 

 marked cases of true diphtheria. The streptococcus and pneumo- 



