INTRODUCTION. 9 



bacteria most frequently met with in some of the forms of 

 putrefaction. 



It must be remembered however that this is not the only 

 organism that gives rise to the butyric acid fermentation ; 

 several other bacteria, differing most markedly in many of 

 their features from the Clostridium butyricum, generally, 

 however, like that organism, carrying on their work in the 

 absence of free oxygen, have the power of setting up alone, 

 or in conjunction with the Clostridium butyricum, the 

 butyric fermentation. In ripened cheese, part of the flavour 

 at any rate is due to the products formed in the ripening 

 curd in the presence of this organism. 



The lactic acid fermentation so frequently met with 

 in milk, is also the result of the vital activity of several 

 organisms, Pasteur and Lister both describing lactic acid 

 bacteria and micrococci. Hueppe also describes a special 

 bacterium which he says has the power of breaking up milk 

 sugar and saccharose into lactic acid and carbonic acid ; 

 whilst from material taken from the mouth and teeth he 

 succeeded in separating two micrococci, both of which had 

 the power of converting sugar into lactic acid, and by a 

 series of experiments he also proved that certain of the 

 pigment-forming bacteria, such as Bacillus prodigiosus — 

 the organism that gives rise to what is known as bleed- 

 ing bread — supply so much lactic acid as a result of 

 their metabolic processes, that in their presence milk is 

 curdled, the casein being precipitated. Further, even a 

 pathogenic form of micro-organism — micrococcus osteomye- 

 litis — is said by Krause to set up the same reaction. 

 Jorgensen mentions that " Delbruck found that in a mash 

 prepared from dry mould and water, lactic acid was first 

 formed at a temperature of 50° C, and from this he draws the 

 conclusion that in this case the active lactic acid ferment 

 has its maximum temperature at this degree of heat." 

 This is an exceedingly interesting fact, for as Schottelius 

 and Wood have pointed out, as the temperature rises the 

 Bacillus prodigiosus loses its power of forming a pigment, 

 and if it is grown on potato or bread paste for example, 

 in an incubator at blood heat instead of at the temperature 

 of the room, the colour is gradually lost and the culture no 

 longer smells of herring brine, but the power of forming lactic 

 acid from milk sugar, with the accompanying precipitation 



