MICROCOCCUS ZYMOGENES 231 



with the M. aureus, is stated by these authors to be 

 perfectly distinct from the foregoing. Other organisms 

 which are occasionally met with in abscesses, the Staphylo- 

 coccus cereus albus and S. cereus flavus of Passet, form 

 shining waxy growths on agar, and do not liquefy gelatin, 

 and are probably variants of another species, which may 

 be termed the Micrococcus cereus. 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. Andrewes and Gordon 

 give a differential Table (see p. 230) 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 clouded 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 trans- 

 formed into a turbid liquid with a reddish colour through- 

 out. These changes in milk are characteristic of the 



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



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



