MIXED INFECTIONS. 31 



phenomena of infectious diseases are referable to 

 mixed, secondary or superimposed infections. 



Two exogenous infections may attack an indi- 

 vidual at the same time. Measles and scarlet fever 

 and diphtheria and scarlet fever have been known 

 to coexist. Pneumococcus pneumonia and typhoid 

 fever, chancre and soft chancre with pus cocci, 

 syphilis and gonorrhea, diphtheria with strepto- 

 cocci, tetanus with gangrene-producing organisms, 

 are common observations. One organism may in- 

 tensify the virulence of another. Diphtheria ac- 

 companied by streptococcus infection seems to be 

 more virulent than diphtheria alone. It is also 

 believed that the presence of aerobic organisms 

 (those which demand oxygen for their develop- 

 ment) in a wound infected with the tetanus bacil- 

 lus or the bacillus of malignant edema (anaerobic 

 organisms), may increase the virulence of these 

 infections. Streptococci are probably important 

 organisms in scarlet fever, for they are present in 

 unusual numbers in the throat lesions and are 

 often found in fatal cases in all the organs, yet it 

 is possible that they inaugurate only a mixed or 

 secondary infection superimposed on that of the 

 scarlatina virus. The conditions are somewhat 

 similar in smallpox, the pustules of which invari- 

 ably contain streptococci, staphylococci, or both. 

 In both scarlatina and smallpox these secondary 

 infections may be responsible for many fatalities. 



Pneumococcus pneumonia occurring during the 

 course of, or during convalescence from the erup- 

 tive fevers, diphtheria, typhoid fever or erysipelas ; 

 a streptococcus septicemia developing during 

 typhoid (giving rise to an irregular temperature 



