THE GENUS MICROCOCCUS 219 



The third principal type of the micrococci is the non- 

 liquefying form. In our series of one hundred and four- 

 teen cultures, twenty-five belonged to this type. In two 

 points slight, but possibly significant, differences appear 

 between the non-liquefying micrococci and those previ- 

 ously considered. The Gram stain was more often posi- 

 tive with the non-liquefiers; both slides remained colored 

 in eight cases, in eleven more the result varied, while only 

 six were consistently negative. Again, with these forms the 

 pigment produced had a distinctly orange tinge in certain 

 cases. Nine of the twenty-five cultures showed a color 

 falling in the upper part of the Orange Yellow column of 

 the Frontispiece, and one was in the upper part of the 

 Cadmium Orange. In both respects these strains resem- 

 ble the genus Aurococcus, and form connecting links 

 with Aur. aurantiacus. Some of our strains might well 

 be considered weakened forms of the latter. Others, on 

 the contrary, were apparently vigorous saprophytic forms 

 with a clear lemon-yellow growth, and the number of cases 

 in which non-liquefying yellow saprophytic cocci have 

 been isolated by other observers makes it probable that 

 the type is a real, and not uncommon, one. 



The earliest yellow coccus to be characterized was the 

 Micrococcus luteus of Cohn (1872). It was, of course, 

 not isolated in pure cultures; its growth was observed 

 on potato and in a solution of ammonium acetate. The 

 color and morphology alone were noted, altho it was 

 stated that the pigment was soluble in water. Chester 



