62 MICRO-ORGANISMS AND DISEASE. [CHAP. 



pigment of various colours. They grow well at ordinary 

 temperatures, and occur chiefly as zoogloea ; they differ from 

 one another by forming different pigments. The thicker the 

 layer the more marked is the pigment. This is either 

 soluble in water or it is insoluble, in the latter case it re- 

 mains limited to the cells and their interstitial substance. 

 The cells are spherical (Micrococcus prodigiosus, chlorinus, 

 fulvus) or slightly elliptical (M. luteus, auriantiacus, cyaneus, 

 violaceus). They are all aerobic and produce this pigment 

 only when there is free access of air. They grow best on 

 boiled potato, bread, paste, and boiled-egg albumen. They 

 can be transplanted, and always produce the same pigment. 

 When growing and kept in the depth of a solid nourishing 

 material, i.e. removed from the free surface, they grow as 



FIG. 16. OVAL MICROCOCCI WHICH POSSESS A BLUE COLOUR, MICROCOCCUS 

 CYANEUS, SINGLY AND IN DUMB-BELLS. 



colourless micrococci. They abound in the air in some 

 localities and at certain seasons more than at others, (a) 

 Micrococcus prodigiosus is blood-red, the colour is lodged 

 not in the micrococci but in the interstitial substance, and 

 is insoluble in water, soluble in alcohol ; it occurs chiefly as 

 zoogloea, in the shape of smaller or larger droplets. The 

 cells are the smallest of all pigment-micrococci. (ft) Micro- 

 coccus luteus is yellowish, and the pigment is insoluble in 

 water. It occurs also in fluid nourishing material, forming 

 a pellicle. I have met with it in the air, and have sown it 

 in fluid pork-broth, where it -grew very abundantly at a 

 temperature of 32 to 38 C. It was found as single cells 

 or dumb-bells, and formed a thick pellicle on the surface, 



