140 BACTERIOLOGY. 



aureus) forms a golden-yellow pigment, induces 

 suppuration, and in sugar solutions produces 

 lactic acid ; the comma bacillus of Asiatic chol- 

 era causes disease in man, forms in its growth 

 upon potato a yellowish brown pigment, and in 

 sugar solutions produces Isevo-rotatory lactic 

 acid ; the common bacillus of the colon (B. colt 

 communis) as a rule lives a harmless sapro- 

 phytic existence in the intestine, but may also 

 cause serious illnesses and inflammations, 

 while in sugar solutions it can effect a lactic 

 acid fermentation, and when grown on potato 

 forms a dirty brown pigment. B. prodigiosus 

 produces red spots upon substances rich in 

 starch, such as potatoes or wafers, a phenome- 

 non which in early times was regarded as the 

 miracle of the bleeding host ; when grown at 

 higher temperatures it brings about vigorous 

 lactic acid fermentation without any produc- 

 tion of pigment. The mere fact that it is pos- 

 sible to obtain parasitic or zymogenic germs 

 in pure culture, and to cultivate them as 

 harmless saprophytes upon various lifeless 

 nutrient media shows that it is impossible to 

 divide bacteria into physiological species ac- 

 cording to their mode of action. 



This is practically opposed to the ideas 

 which were expressed cautiously by Ferdinand 

 Cohn and Schroter, and more outspokenly by 



