182 BACTERIOLOGY 



there is found the Oidium lactis, described with considerable 

 completeness by Grawitz, which forms a white fur like a 

 mould. The fibres of the mycelium mount upwards, be- 

 come segmented, and support rows of cylindrical gonidia. 

 The oidium grows on gelatine without liquefying it, and 

 forms a white, long-haired fur on the suface of the plate at 

 20" C, diffusing at the same time an odour as of sour milk. 

 The thrust-culture appears permeated with fibres. Gela- 

 tine which has an acid reaction is liquefied. Whitish stars 

 develop on agar at 30° C, which coalesce and cover the 

 surface. Growth takes place also on serum, and on milk a 

 thick coating of mould forms. (See fig. 5.) 



Bacillus butyricus. — According to Hueppe the butyric 

 acid fermentation is caused by this bacillus, which consists 

 of short curved rods endowed with a lively motility. They 

 have the power of curdling milk, and originate the above- 

 named variety of fermentation. The- curdled caseine is 

 dissolved and converted into peptone with simultaneous 

 splitting off of ammonia and other products of division, the 

 milk acquiring at the same time a bitter taste. Gelatine is 

 very rapidly liquefied. Yellowish colonies appear on plates ; 

 in thrust-cultures a greyish-white skin develops, and also a 

 yellow coloration of the liquefied gelatine, while on agar a 

 yellow layer is formed, and a wrinkled, dirty coating upon 

 potato. Centrally- situated spores develop at incubation 

 temperature. 



A genuine Bacillus butyricus is, according to Botkin, to 

 be met with in all milk, and by the liberation of free butyric 

 acid causes raj)id curdling with abundant evolution of gas. 

 To isolate it, the milk is sterilised for half an hour in the 

 steam steriliser and, after being sealed up air-tight, is de- 

 posited in the incubator. It is comjpletely decomposed in 

 two weeks, and is then used to make an anaerobic plate- 

 culture, best done, according to Botkin, by employment of a 



