288 A MANUAL OF BACTERIOLOGY 



Cultural reactions. The Hofmann bacillus develops 

 well at temperatures from 20 to 37 C., and is almost a 

 strict ae'robe ; there is no growth anaerobically in hydrogen. 

 On serum, agar, and gelatin it forms cream-coloured colonies 

 or growths, barely distinguishable from those of the Klebs- 

 Loffler bacillus ; gelatin is not liquefied. On ordinary 

 potato it hardly grows at all, what growth there is being 

 quite invisible. On alkaline potato, 1 however, it forms 

 distinct cream-coloured colonies, usually visible by the 

 second day. Tn stab-cultures in gelatin and glucose-agar 

 no gas is formed, and the growth is confined to the upper 

 part of the stab. In broth it forms sometimes a granular 

 deposit, sometimes a general turbidity. On neutral litmus 

 glucose-agar and in litmus milk a blue colour is developed, 

 indicating the production of alkalinity ; milk is not 

 curdled. Cultivated in peptone water an indole-like 

 reaction with sulphuric acid alone can be obtained after 

 a variable time, three to four weeks, while the diphtheria 

 bacillus gives it in about a week ; with a nitrite and 

 sulphuric acid the indole-like reaction can be obtained with 

 both the pseudo- and diphtheria bacilli in about a week. 

 The substance giving this indole-like reaction is not indole, 

 but skatole-carboxylic acid. 2 A broth culture reduces a 

 weak solution of methylene blue. The Hofmann bacillus 

 is non-pathogenic to guinea-pigs in doses of 5 c.c. or more 

 of a forty- eight hours' broth culture, but is virulent to 

 certain birds (see below, p. 290). Mandelbaum and Heine- 

 mann 3 state that if a glycerin- agar plate be smeared with 

 human blood and inoculated, the diphtheria bacillus 

 produces colonies surrounded by a yellow zone, while the 

 colonies of the Hofmann and xerosis bacilli do not change 



1 Ordinary potato rendered alkaline with a 10 per cent, solution of 

 sodium carbonate before sterilisation. 



2 Hewlett, Trans. Path. Soc. Land., vol. li, 1900, p. 187 ; vol. lii, 

 1901, p. 113. 



3 Centr. f. Bakt. (Orig.), liii, 1910, p. 356. 



