350 BACTERIOLOGY. 



contracting the disease. It is, therefore, apparent that 

 infection in diphtheria, as in other infectious diseases, 

 requires not only the presence of virulent bacilli, but 

 also a susceptib lity to the disease, which may be 

 inherited or acquired. Among the predisposing in- 

 fluences which contribute to the production of diph- 

 theritic infection may be mentioned the breathing of 

 foul air and living in overcrowded and ill-ventilated 

 rooms, poor food, certain diseases, more particularly 

 catarrhal inflammations of the mucous membranes, and 

 depressing conditions generally. Under these condi- 

 tions an infected mucous membrane may become sus- 

 ceptible to disease. In connection with Beebe (1894) 



1 made an examination of the throats of 330 healthy 

 persons who had not come in contact, so far as known, 

 with diphtheria, and we found virulent bacilli in 8 only, 



2 of whom later developed the disease. In 24 of the 330 

 healthy throats non-virulent bacilli or attenuated forms 

 of the diphtheria bacillus were found. Very similar 

 observations have been made by others in many widely 

 separated countries. 



The Persistence of Diphtheria Bacilli in the Throat. 

 The continued presence of virulent diphtheria bacilli 

 in the throats of patients who have recovered from the 

 disease, and after the disappearance of the exndate, has 

 been repeatedly demonstrated. Beebe and I found that 

 in 304 of 605 consecutive cases the bacilli disappeared 

 within three days after the disappearance of the pseudo- 

 membrane; in 176 cases they persisted for seven days, 

 in 64 cases for twelve days, in 36 cases for fifteen days, 

 in 12 cases for three weeks, in 4 cases for four weeks, 

 and in 2 cases for nine weeks. Since then 1 have met 

 with a case in which they persisted for six months. 



