462 COR YNEBA CTERI UM 



as regards the inoculation of filtrates, or of killed cultures, though our own results were far 

 less uniform than those recorded by Bongert. It would appear that this organism produces 

 an exotoxin which is fatal for mice. According to Bongert this toxin is relatively heat- 

 stable, since it withstands heating for 2 hours at 55° C, or for a few minutes at 74° C. ; 

 but the particulars given are not sufficiently precise to allow of any definite conclusion with 

 regard to the time or temperature required for inactivation. 



The toxin of this organism has not, so far as we are aware, been compared with that 

 of C. diphtherice or of C. ovis, but it seems exceedingly unlikely that there is any relationship, 

 since the mouse is conspicuously resistant to diphtheria toxin, and the guinea-pig and 

 rabbit, which are very susceptible to C. ovis, are resistant to C. murium. 



It may be noted that Fischl, Koech and Kussat (1931) described an organism under 

 the name of Corynebacterium arthritidis muris, which they isolated from the swollen ankle 

 joint of a, white mouse. On inoculation into the joints of normal mice and rats it gave 

 rise to a similar arthritis. Little is known about this organism, but it appears to- differ 

 in some respects from C. murium. 



There remains C. acnes, a diphtheroid organism described in the lesions of 

 cutaneous acne by Unna (1896). It was first isolated by Sabouraud (1897), and has 

 since then been studied by Gilchrist (1900, 1903), by Fleming (1909), and by Siid- 

 mersen and Thompson (1909-10). Its claim to pathogenicity must rest in the 

 main on its constant association with the disease in man. Siidmersen and Thompson 

 state that the two strains examined by them were pathogenic for the mouse but 

 not for the guinea-pig ; but their description of the lesions in the latter animal is 

 extremely scanty. C acnes is clearly marked as a distinct species from those 

 described above by its peculiar growth requirements (see p. 471) and particularly 

 by the fact that it is microaerophilic. 



C. typhi, another microaerophilic diphtheroid, was isolated by Plotz (1914) 

 from the blood in typhus fever. It is now generally admitted to be an example 

 of a parasitic diphtheroid with no established pathological role (Olitsky 1921). 



The Gravis, Mitis and Intermedius Types of C. diphtheriae. 



Attention has already been drawn on p. 450 to the recognition by McLeod 

 and his colleagues at Leeds (Anderson, Happold, McLeod and Thomson 1931) of 

 three stable varieties of the diphtheria bacillus — the gravis, intermedius and mitis 

 types. The characters of these three types, as recorded by Robinson (1934, 1940), 

 and Cooper, Happold, McLeod and Woodcock (1936), are summarized in Table 30. 



This summary can do no more than serve as a guide to the recognition of the 

 three types. On the whole the characters of the intermedius type are the most 

 constant. In the identification of gravis strains starch fermentation is of particular 

 value since, though it may be delayed beyond 24 hours, it is seldom absent. 



Sometimes it is difiicult to distinguish not only between the three types, but 

 between diphtheria bacilli and diphtheroids. Each of the types has one or more 

 species of diphtheroid bacilli that closely resemble it. Space does not permit a 

 detailed description of the differential characters of these organisms. In general, 

 it will be found that the diphtheroid bacilli tend morphologically to be more regular 

 in shape, size, depth of staining, distribution of bars or granules, and arrangement ; 

 diphtheroids lie often in palisades, whereas true diphtheria bacilli show the Chinese 

 letter type of distribution, or, if they are in bundles, they have seldom the same 

 regularity of arrangement as that of diphtheroids. The colonial differences are 

 often very slight and, as they vary from one medium to another, they can be 

 learned only by close observation and long experience. 



