THE BIOLOGY OF MICROBES, ETC. 117 



ultimately coalesce into equal-sized patches. On 

 fluid media they form an orange-coloured pellicle. 

 M. aurantiacus also grows on steamed potatoes and 

 white of egg. The pigment is soluble in water. 



Micrococcus fulvus. Cells 1/5 fi in diameter; 

 they form rusty-red drops and gelatinous masses 

 on horse-dung. 



Micrococcus violaceus. The cells are 1*4 JJL in 

 diameter, and occur as bright violet-coloured gela- 

 tinous drops or patches on the surface of steamed 

 potatoes exposed to the air. 



Micrococcus cyaneus. The cells are elliptical and 

 grow on potatoes and fluid media, giving rise to a 

 blue pigment when in contact with air. The pig- 

 ment is soluble in water, and the solution is at first 

 green, but afterwards becomes an intense blue. 

 Acids convert this pigment into a red colouring 

 matter, while alkalies turn it green. There are no 

 characteristic absorption bands shown when a solution 

 of the blue pigment is examined by the spectroscope. 



Micrococcus rosaceus. The cells are from 1 to 1*5 

 fjL in diameter, and give rise to a rose-coloured growth 

 on the surface of nutrient gelatine and agar-agar. 



Micrococcus cinnabareus. This microbe grows very 

 slowly on the surface of gelatine. At the end of 

 eight days the colonies appear as small drops of 

 a red colour ; but ultimately the colour becomes 

 red-brown. This microbe occurs in twos, threes, and 

 fours ; and very rarely as an isolated coccus. The 

 pigment is soluble in water. 



Micrococcus hcematodes. This microbe is some- 

 times found in human sweat. It grows on steamed- 



