328 APPLIED BACTERIOLOGY 



fusions of rotting vegetables and animal substances, form- 

 ing small tufts and floating masses. On gelatine plates it 

 forms small yellowish dots surrounded by a brownish halo 

 which extends more and more over the gelatine. On 

 reaching the surface it appears as a small brownish button 

 surrounded by a very brown halo, and a depression due to 

 the slow liquefaction of the gelatine. On agar it grows 

 at 35° C, as a thick shining expansion, which adheres so 

 closely to the medium that it is impossible to remove it 

 without carrying away some of the agar. The growth has 

 a tendency to form concentric rings. Sometimes the 

 growth becomes covered with a grayish efflorescence, which 

 is dry and very brittle. The agar becomes brown in colour. 

 All the cultures have a very strong mouldy smell. 



FERMENTATION. 



The term ' fermentation ' is derived from fervere, to boil, 

 and was formerly applied to all those cases where a liquid 

 or semi-liquid mass was seen to become puffed up and to 

 disengage gas without any apparent cause, among the 

 earliest observed forms of this phenomenon being the 

 fermentation of grape-juice and the leavening of bread. 

 Owing to the mystery with which these well-known pro- 

 cesses were surrounded, the term gradually came to be 

 applied to all those chemical processes which were brought 

 about by the presence of a body known as a ferment, the 

 presence of which' was indispensable, as the necessity for 

 its presence was unintelligible. The meaning of the term 

 ' fermentation ' has now been much extended, until at the 

 present day we mean those chemical changes which take 

 place in a substance through the agency of a body derived 

 from the animal or vegetable kingdom, termed a ferment. 



