448 CORYNEBAOTERIUM 



to be sure that Reymond, and Kuschbert and Neisser, were dealing with a single 

 bacterial species. It is, moreover, equally impossible to identify with certainty 

 any of the strains now labelled C. xerosis with those described in the early 'eighties. 

 The stage of technical development that bacteriology had then reached did not 

 permit each new organism that was isolated to be fully studied and described. 

 The importance of C. diphtherice as a human pathogen focussed attention on the 

 differentiation of the species from others with which it might be confused. Our 

 picture of the type species thus became more and more complete as time went 

 on ; but to the related diphtheroids little attention was paid beyond that 

 necessary to determine their probable relation to the diphtheria bacillus itself. As 

 Andrewes and his colleagues point out it is extremely difficult to determine which 

 of the strains, to which specific names have from time to time been assigned, 

 represent well-differentiated species. Some of those who have reviewed the group 

 as a whole have been liberal in the distribution of titles (Graham-Smith 1908, 

 Mellon 1917, Eberson 1918, Chalmers and Macdonald 1920). Here, as elsewhere, 



we propose to adopt a conserva- 



^ \-^ tive view, and to list as species only 



, - those organisms which have been 



■w^ _, adequately described, and appear 



from this description to be reason- 

 ably well-differentiated. In discussing 

 this question of classification and 

 nomenclature in greater detail we 

 may consider C. diphtherice as a 

 species, since it has in fact been so 

 regarded in most of the observations 

 to which we shall refer. Recent work 

 has, however, shown that it is divisible 

 into three well-differentiated types, 

 and that this differentiation is of 

 considerable importance from the 

 medical point of view. The discussion 

 of this particular problem may, how- 

 ever, conveniently be dealt with in a 

 separate section. 

 Habitat. 



Though attention has in the past been concentrated almost entirely on the 

 parasitic members of the Corynehacterium group, which live mainly on the skin 

 and mucous surfaces of their animal host, there is reason to believe that some 

 members are adapted to the saprophytic life. Diphtheroid bacilli are common in 

 heated milk products (Mattick 1944), and appear to occur also in the soil. Many 

 of the parasitic species are pathogenic, others form an important constituent of 

 the normal bacterial flora of various hosts. 



Morphology. 



The club-form, from which the name is derived, is only one of many shapes which 

 may be assumed by the individual cells of the type species, C. diphtherice. This 

 organism is indeed characteristically pleomorphic. One of the most typical forms 

 (see Fig. 82), in films prepared from a 24-hours' culture on Loeffler's serum, is that of a 



