C. XEROSIS 467 



Fig. 86). The bacilli are more tenacious of the Gram stain than C. diphtherice, or 

 than many other diphtheroids. 



Growth. — On Loefjler^s serimi, after 24 hours at 37° C, C. hofmanni produces 

 colonies which are larger than those of C. diphtherice, and whiter in colour. They 

 vary in diameter from 1 to 1-5 mm., and are circular, convex, smooth, and opaque, 

 with an entire edge. They are homogeneous in structure, butyrous in consistency, 

 and emulsify readily. After 48 hours they increase in size to a diameter of 2 mm. 

 or so, and the edge may become slightly erose. On agar this species, unlike C. diph- 

 therice, grows readily and abundantly, forming colonies very similar to those produced on 

 serum. In contrast to C. diphtherice, a confluent growth often occurs in primary cul- 

 ture, or in early subculture. In broth a moderate turbidity is produced, the growth 

 gradually setthng to the bottom as 

 a powdery deposit. No pellicle is 



formed. In agar or in gelatin stab C. ^' » 



hofmanni produces little growth along . ' "^ 



the needle track, but a profuse sur- ^-'•'*,% . •"'/»., 



face growth. C. hofmanni is aerobic » _. ^r^<^^ "^ i<- '*^ - 



and facultatively anaerobic ; the opti- ■ ^ * ' . J c' '<* -'r v- 



mal temperature for growth is in the '^ r' * ^ '' < \ » ^ ■» 



neighbourhood of 37° C. The resist- v "" / " . T^'si* ^' f • < ^ • . 



ance of this species to heat, or to *^ ■**■%-' n*' '.> t-^ ' ■* '' \ 



antiseptics, has not been systemati- ~ ' ^~ j" ^ "^ ** "a' O •' *"•-' 



cally examined, but there is no ' ,- - * '^ '"-''*» '"" •**■%.- 



evidence that it differs in these re- -.^ ^. '^ > *% ' c - , x ' 



spects from the type species. ''•' '' ' *» ''^■> 



Biochemical Reactions. — C. hof- . , ,^^ '.^ ,,»»w j^ ,. 



manni ferments none of the carbohy- •.•^»y^ ' ^ '^ •-■■ 



drates against which it has been tested, ^ * « ,'' x" 



and these include all those referred to ' . ^ r ) ' 



in the case of C. diphtherice. It pro- 

 duces no change in litmus milk, does 



, f c 1 i- J J i Fio. 86. — C. hofmanni. 



not liqueiy gelatm, and does not ■' 



produce indole. Nitrates are reduced. From 24-hours' culture on Loeffler's serum ( X 1000). 

 It does not produce haemolysis. 



Antigenic Structure. — All that is known on this point is that the antigenic make- 

 up of such strains of C. hofmanni as have been examined differs entirely from that 

 of C diphtherice on the one hand, and from C. xerosis on the other. 



Toxin Prodoction and Pathogenicity. — C. hofmanni produces no toxin and is 

 not pathogenic. 



C. xerosis 



An organism which possessed certain of the characters which we ascribe to G. xerosis 

 was isolated from the conjunctiva by Reymond in 1881, and described somewhat more 

 fully in 1883. The first detailed description of this organism was provided by Kuschbert 

 and Neisserin 1883, if we may assume that these three records in fact refer to the same 

 bacterial species. The original view, that C. xerosis was setiologically related to a par- 

 ticular conjunctival lesion, has been generally abandoned. Griffith (1901) states that 

 this organism is the commonest bacterial inhabitant of the normal conjunctival sac. 

 Andrewes and his colleagues record their doubt as to whether C. xerosis is even now suffi- 

 ciently well characterized to deserve specific rank ; and their scepticism appears fully 

 justified. The description which follows must be regarded as summarizing the characters 

 of those strains to which most observers would allot this particular name. 



Morphology. — The form assumed by C. xerosis, in films from a culture grown on 



