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; 
benzoie, 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 
