Micrococcus. 7 



What I have said above of the distinctions of the species is especially 

 true of this genus. The accepted species of Micrococcus show very 

 little or no difference in form and size, and there remains only chemical 

 action as a means of separating the species, which is therefore treated 

 somewhat fully. 



A. CHROMOGENOUS SPECIES. 



i. M. prodigiosus, Cohn (I.e., p. 153). 

 Monas prodigiosa, Ehrenberg. 

 Palmella prodigiosa, Mont.; Cooke, "British Fresh- 

 water Algae," p. 12. 

 Zoogalactina imetropha, Sette. 

 Bacteridium prodigiosum, Schroter. 



Cells round or oval, colour- 

 less, about "5-1 p,* in diameter; 

 forming at first rose-red, then 

 blood-red, at last pallid gela- 

 tinous masses. (Fig. i.) 



On nitrogenous substances, 

 e.g. on boiled potatoes, meat, 

 wheat-bread, white of egg, starch- . * 



Fig. i. Micrococcus prodigwsus, 

 paste, etC. Cohn, X 1200 (from nature). 



M. prodigiosus is that organism which produces the long-known 

 peculiar appearance, formerly designated " blood-rain," on bread, on 

 the "host," etc. It forms at first little rose-red points and heaps, 

 which by degrees increase to rounded bright-red spots, and afterwards 

 become confluent into widespread, even dripping, blood-red patches. 

 These consist of a red-tinted mucous mass, in which thousands of 

 millions of Micrococcus cells are embedded. These cells are them- 

 selves colourless, but they secrete the red colouring matter in the 

 mucus. This colouring matter is very similar to fuchsin in its physical 

 and chemical relations. It is not soluble in water, but completely so 

 in alcohol ; the solution, evaporated and again dissolved, is orange- 

 red ; the colour is changed by acids into a bright carmine, by alkalies 



* i n (pronounced mu) = -ooi mm. = 5^3 of an inch, nearly. 



