66 BACTERIOLOGY. 



coagulating milk with neutral reaction, independent of 

 acids are found not infrequently among bacteria. The 

 B. prodigiosus, for instance, in from one to two days 

 coagulates to a solid mass milk which has been steril- 

 ized at 55 to 60 C. These ferments have not been 

 thoroughly investigated: they are probably present, 

 however, in all species of bacteria which coagulate milk 

 with the production of acid. 



Fermentation yields products that are poisonous to 

 the ferment; hence fermentation ceases when the nu- 

 triment is exhausted or the fermentation is in excess. 

 Different kinds of fermentation obtain specific names, 

 according to product. Thus acetic, yielding acetic 

 acid; alcoholic or vinous, yielding alcohol; ammoniacal, 

 yielding ammonia; amylic, yielding amylic alcohol; 

 benzole, yielding benzoic acid; butyric, yielding butyric 

 acid; lactic, yielding lactic acid; and viscous, yielding 

 a gummy mass. 



Pigment Production. Pigments have been little chem- 

 ically studied, but the recent investigations of Klein 

 and Migula, Thumm and Schneider, and others throw 

 some light on the subject. They have no known im- 

 portance in connection with disease, but are of interest 

 and have value in identifying bacteria. 



RED AND YELLOW PIGMENTS. Of the twenty-seven 

 red and yellow bacteria studied by Schneider, almost 

 all produce pigments soluble in alcohol and insoluble 

 in water. The larger majority of these possess in com- 

 mon the property of being colored blue-green by sul- 

 phuric acid and red or orange by a solution of potash. 

 Though varying considerably in their chemical compo- 

 sition and in their spectra, they may be classified, for 

 the most part, among that large group of pigments 



