C. DIPHTHERIA 465 



strain, and assigning to each character a weight which experience alone can provide, 

 that a sound conclusion on its identity can be reached. Valuable help will be 

 obtained by a careful study of McLeod's (1943) review. 



The Classification of Corynebacteria. 



It will be obvious from the foregoing discussion that the time has not yet arrived 

 to attempt any general systematic classification of the large number of different 

 types of corynebacteria that have been described. Certain organisms have, how- 

 ever, been studied in sufiicient detail to make it clear that they deserve specific rank. 

 Among these the type species, C. diphthericB, is of course pre-eminent. Among the 

 non-pathogenic species parasitic to man C. hofmanni is a well-recognized species, 

 and C. xerosis would probably fall into the same category. We follow Andrewes 

 and his colleagues (1923) in excluding the so-called C. coryzcB segmentosmn from the 

 list of identifiable species. Including the various species and types, of human or 

 animal origin, that have been dealt with above, this leaves us with the following 

 named species within the genus : C. diphthericB (types, gravis, mitis and intermedins), 

 C. hofmanni, C. xerosis, C. ovis, C. pyogenes, C. equi, C. renale, C. murium, C. acnes 

 and C. typhi. For the rest, we are in entire agreement with Andrewes and his 

 colleagues in believing that specific names should be withheld from the numerous 

 diphtheroids that have been described until they have been examined in greater 

 detail and their identity more fully established. 



We append a summarized description of the named species, and a tabular descrip- 

 tion of the fermentation reactions of the eleven types of diphtheroid bacilli differenti- 

 ated by the Committee of the Medical Research Council (see Andrewes et al. 1923). 

 Reference may also be made to a paper by Brooks and Hucker (1944), who divided 

 79 strains of animal diphtheroids into 3 groups on the basis of growth and 

 biochemical reactions. 



C. diphtherise 



Observed by Ivlebs (1883); isolated and described by Loeffler (1884). 



The morphology and staining reactions of this species have been described above, and 

 the absence of motility and capsulation, common to the genus, has been noted. 



Type of Growth. — On Loeffler's serum, the colonies, after 24 hours' incubation at 

 37° C, are about 1 mm. in diameter, circular, convex, with a slightly raised centre, a 

 smooth or finely granular surface and an entire edge ; granular in structure when viewed 

 by transmitted Ught, butjTous in consistency, pale or deeper cream in colour, moderately 

 opaque, and easily emulsifiable in water or saline. After 48 to 72 hours' incubation the 

 colony shows a varying degree of enlargement, the centre becomes more raised, more 

 opaque, and deepens in colour, while the periphery remains fiat, extends outwards and 

 appears more transparent than the centre, giving the so-called " poached-egg " appearance. 



On agar, growth is much less abundant, and the individual colonies are, for the most 

 part, smaller, often having a diameter of 0-25 mm. or less, after 24 hours' incubation at 

 37° C. These small colonies, which are greyish-white in colour, convex with a raised cen- 

 tral portion, and usually with an entire margin, are frequently mingled with a few larger, 

 whiter colonies. 



On gelatin, the growth is very similar to that on agar, but develops much more slowly 

 owing to the lower temperature of incubation. In stab culture growth develops along 

 the whole length of the needle-track without lateral outgrowths, and with a slight 

 surface growth consisting of a raised central portion and a flatter periphery, some- 

 times showing an irregular margin. The medium is never liquefied. 



On 'potato, growth is usually very scanty and often invisible to the naked eye. 



