MICROCOCCUS AUREUS 347 



posing the rest of the colony. Microscopically, these colo- 

 nies are composed of small round cells, irregularly grouped 

 together. They are in every way of the same appearance as 

 those seen upon the original cover-slip preparation. 



Prepare from one of these colonies a pure stab-culture in 

 gelatin. After thirty-six to forty-eight hours liquefaction 

 of the gelatin along the track of the needle, most conspicu- 

 ous at its upper end, will be observed. As growth continues 

 the liquefied portion becomes more or less of a stocking- 

 shape, and gradually widens at its upper end into an irregular 

 funnel. This will continue until the whole of the gelatin 

 in the tube eventually becomes fluid. There can always be 

 noticed at the bottom of the liquefying portion an orange- 

 colored or yellow mass composed of a number of the organ- 

 isms which have sunk to the bottom of the fluid. 



On potato the growth is quite luxuriant, appearing as a 

 brilliant, orange-colored layer, somewhat lobulated and a 

 little less moist than when growing upon agar-agar. 



It does not produce fermentation with gas production. 



It belongs to the group of facultative anaerobes. 



In .milk it causes coagulation with acid reaction. This 

 is, however, variable. 



It is not motile, and being of the family of micrococci 

 does not form endogenous spores. It possesses, however, 

 a degree of resistance to detrimental agencies that is some- 

 what greater than that common to non-spore-bearing 

 bacteria. 



In bouillon it causes a diffuse clouding, and after a time 

 a yellow or orange-colored sedimentation. 



This organism is the commonest of the pathogenic bacteria 

 with which we shall meet. It is micrococcus aureus, or as 

 it is more commonly known, the staphylococcus aureus, 



