422 DIPHTHERIA 



to produce small quantities of toxin ; and in the case of others 

 again, where no toxin -production can be demonstrated directly, the 

 injection of a nitrate of a broth culture has given rise to antitoxin 

 formation, though in small degree. These facts show that all 

 degrees both of virulence and of toxin-production are met with. 



Diphtheria Carriers. It has been known for some time 

 that diphtheria bacilli may persist for considerable periods in 

 the throats of those who have suffered from the disease, and 

 repeated examinations may be necessary before these persons 

 can be pronounced free from the organisms and thus devoid of 

 danger to the community. In such circumstances the bacilli 

 often become attenuated, but this does not appear to be always 

 the case. More recently it has been established that during 

 the occurrence of diphtheria the bacillus may be found in the 

 throats of those who have been in contact with the patients and 

 that accordingly these individuals may act as carriers of infection. 

 This is no merely occasional occurrence, as the observations of 

 Macdonald in this country and of Kenyoun in America, which 

 taken together include the examination of over three thousand 

 contacts, show that about 10 per cent, of those harboured the 

 diphtheria bacillus. Some of the " carriers " suffer from slight 

 indisposition, sore throat, etc., but others have no clinical 

 symptoms at all. The carriers may be of all ages and the 

 bacilli obtained from them prove, in some instances, to be still 

 virulent for weeks or even months after exposure to infection. 

 The discovery and control of such carriers clearly come to be 

 very important factors in preventing the spread of the disease. 



BACILLI ALLIED TO THE DIPHTHERIA BACILLUS. 



It is now recognised that the diphtheria bacillus is a member of 

 a group of organisms with closely allied characters which are 

 of common occurrence and have a wide distribution. The terms 

 " pseudo-diphtheria bacilli " and " diphtheroid bacilli " have been 

 applied in a loose way to organisms which resemble the 

 diphtheria bacillus microscopically, especially as regards the 

 beaded appearance. Such bacilli have been obtained from the 

 mouth, nose, skin, genital organs, and even from the blood in 

 certain diseases. They are to be met with sometimes in condi- 

 tions of health, and they have been obtained from many diverse 

 morbid conditions from skin diseases, from coryza, from 

 leprosy, and even from general paralysis of the insane. As 

 has been found with other groups, the differentiation is a matter 

 of considerable difficulty. Some are practically identical with 



