IDENTIFICATION OF DIPHTHEBIA BACILLUS 413 



virulence of recently isolated strains varies enormously, as much 

 as in a proportion of 1 to 400. Some non-virulent diphtheria 

 bacilli have been found 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 filtrate of a broth 

 culture has given rise to antitoxin formation, though in small 

 degree. These facts show how difficult it is to define a true 

 diphtheria bacillus. 



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 

 may become attenuated, but this does not appear to be usually 

 the case. The bacillus may also be found in the throats of those 

 who have been in contact with the patients, and 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 con- 

 tacts, 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 ; 

 in other instances, whilst morphologically and culturally possess- 

 ing the characters of the diphtheria bacillus, they are devoid of 

 virulence. 



Identification of the Diphtheria Bacillus — Allied 

 Organisms. 



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, ear, nose, skin, genital organs, and even from the blood 

 in certain diseases. They are to be met with in conditions of 

 health, and they have been obtained from many diverse morbid 



