MICROCOCCUS ZYMOGENES 275 



There may be many other varieties of micrococci not 

 yet properly differentiated. 1 Well-defined micrococci 

 occur in the saliva (M. salivarius), and in the scurf from 

 the scalp. Andre wes and Gordon give a differential table 

 (see p. 274) of some of these micrococci. 



Micrococcus zymogenes 



Isolated by MacCallum and Hastings 2 from a case of 

 acute endocarditis. A minute micrococcus, non-motile, 

 and staining by Gram's method. On surface agar it 

 forms a thin, slightly elevated, moist, glistening, greyish- 

 white growth. In gelatin stab -cultures the growth is 

 somewhat opaque and granular, with slow liquefaction. 

 Blood-serum is slowly liquefied. On potato a thick, 

 moist, dirty -white growth develops, becoming dry and 

 brownish after three days. Broth becomes slightly 

 cloudy after twenty-four hours' growth, but in three to 

 four days the organisms settle to the bottom, leaving the 

 medium clear. Neither indole nor gas is formed. In 

 neutral litmus milk the litmus is decolorised after a few 

 hours, and in twenty-four hours the milk is firmly curdled. 

 Somewhat later, liquefaction of the curd ensues from 

 above downwards ; at first the turbid fluid is reddish in 

 the superficial layer and yellowish below ; ultimately the 

 whole curd is transformed into a turbid liquid with 

 reddish colour throughout. These changes in milk are 

 characteristic of the organism. It is pathogenic to white 

 mice, hardly so to guinea-pigs and white rats, and mode- 

 rately so to rabbits ; intravenous inoculation into the 

 latter sometimes sets up an endocarditis. Harris and 

 Longcope 3 have reported five more instances of the 

 occurrence of this organism (once from a cesspool, four 



1 See Gordon, Rep. Med. Off. Loc. Gov. Board for 1903-04, p. 388. 



2 Journ. Exp. Med., vol. iv, 1899, p. 521. 



3 Centr.f. Bakt. (Ite Abt.), vol. xxx, 1901, p. 353. 



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