MICROCOCCUS PYOGENES 227 



Inject the M. pyogenes into animals in which the endo- 

 cardium or a bone has been damaged, and in all probability 

 an endocarditis or an osteomyelitis will ensue. The dose 

 and concentration of the organisms are also important 

 factors. Watson Cheyne found that 250,000,000 cocci 

 (M. pyogenes) injected into the muscles of a rabbit pro- 

 duced a circumscribed abscess, but 1,000,000,000 caused 

 a general septicaemia and death. So, probably, while the 

 cells in a healthy wound can dispose of a few organisms, 

 if the latter are abundant or in masses they may gain the 

 mastery. 



Micrococcus pyogenes, var. aureus (Staphylo- 

 coccus pyogenes aureus) 



Morphology and biology. A minute spherical organism 

 measuring about 0'75 //. in diameter. It generally occurs 

 in more or less irregular groups, but may be met with 

 singly or in pairs (Plate I. c). It is non-motile, does not 

 form spores, and stains well with all the anilin dyes and 

 also by Gram's method. It is aerobic and facultatively 

 anaerobic, will develop in vacuo, and grows well and 

 rapidly on all the usual culture media at temperatures 

 from 18 to 37 C. On agar-agar it forms a thickish, 

 moist, shining growth, cream-coloured at first, but after 

 a day or two developing a characteristic orange-yellow 

 colour. It grows in the same manner on blood-serum 

 without liquefaction of the medium. Gelatin is rapidly 

 liquefied, the liquefied gelatin being at first somewhat 

 turbid from yellowish masses of organisms ; these later 

 on subside and form an orange-yellow sediment (Plate 

 I. d) In gelatin plates the colonies form at first small 

 whitish, granular points, developing in two or three days 

 into circular areas of liquefaction with yellowish masses 

 of the organism floating in them. On potato it forms a 



