viii.] BACTERIUM.' 91 



enormous masses in beer that had become sour; it forms 

 dumb-bells, seldom chains of four, and sometimes a pellicle 

 on the surface. Pure cultivations have not been made with 

 it, and before deciding whether it is the real cause of the 

 acetic acid fermentation, experiments with such pure 

 cultures, i.e. inoculations of alcoholic fluids with it, are 

 required. 



3. Pigment Bacteria. Two kinds have been described : 

 Bacterium xanthinum and Bacterium aeruginosum. 



(a) Bacterium xanthinum l is a bacterium about 0*007 to 

 o'oi mm. long, motile, single, also in dumb-bells, or short 

 chains. It produces the yellow colour of yellow milk. Its 

 pigment is soluble in water, and insoluble in alcohol or ether. 

 When introduced into boiled milk of neutral reaction, it 

 multiplies with great rapidity; the milk coagulates after 

 twenty-four hours ; it is soon teeming with them and turns 

 yellow. The reaction of the yellow milk is at first acid, but 

 soon becomes alkaline, and the alkalinity gradually increases. 



(b) Bacterium aeruginosum. In green pus Schrceter dis- 

 covered a bacterium, Bacterium aeruginosum^ The pigment 

 is greenish, and not lodged in the cells themselves ; it is 

 easily diffusible. 



4. Pathogenic Bacteria. Three kinds are described ; the 

 bacteria of Koch's septicaemia, of Davaine's septicaemia, and 

 of fowl-cholera. 



(a) Bacterium septicaemia (Koch). By injecting into 

 rabbits water from the rivulet Pauke, and from putrid mutton, 

 Koch 3 succeeded in producing a rapidly fatal septicaemia, 



1 Schroeter, Biol. d. Pflanzen, ii. p. 120; Vibrio synxanthus, 

 Ehrenberg. 



2 Loc. cit. p. 122. 



3 Mitth. aus d. k. Gaundh. 1881. 



