216 INFLAMMATION AND SUPPURATION 



characterised by the fact that it divides in two planes at right angles to 

 one another (Fig. 54), and is thus generally found in the tissues in groups 

 of four, or tetrads, which are often seen to be surrounded by a capsule. 

 The cocci measure 1 ^ in diameter. They stain readily with all the 

 ordinary stains, and also retain the stain in Gram's method. 



It grows readily on all the media at the room temperature. In a 

 puncture culture on peptone-gelatin a pretty thick whitish line forms 



along the track of the needle, 

 whilst on the surface there is 

 a thick rounded disc of whitish 

 colour. The gelatin is not 



l liquefied. On the surface of 



agar and of potato the growth 

 *j " is an abundant moist layer of 



^ ' ^ ' 4t M the same colour. The growth 



W * * * * on all the media has a peculiar 



^ ., viscid or tenacious character, 



Jk * owing to the gelatinous charac- 



' j j 1er of the sheaths of the cocci. 



J* White mice are exceedingly 



t > susceptible to this organism. 



f Subcutaneous injection is 



jt ' followed by a general septi- 



^ * csemia, the organism being 



X< & \ found in large numbers in the 



blood .throughout the body. 

 Guinea-pigs are less suscep- 



FIG. 54. Micrococcus tetragenus ; young tible ; sometimes only a local 

 culture on agar, showing tetrads. abscess with a good deal of 



Stained with weak carbol-fuchsin. x 1000. necrotic change results ; some- 

 times there is also septicaemia. 



Experimental Inoculation. We shall consider chiefly the 

 staphylococcus pyogenes aureus and the streptococcus pyogenes, 

 as these have been most fully studied. 



It may be stated at the outset that the occurrence of suppura- 

 tion depends upon the number of organisms introduced into the 

 tissues, the number necessary varying not only in different 

 animals, but also in different parts of the same animal, a 

 smaller number producing suppuration in the anterior chamber 

 of the eye, for example, than in the peritoneum. The virulence 

 of the organism also may vary, and corresponding results may 

 be produced. Especially is this so in the case of the strepto- 

 coccus pyogenes. 



The staphylococcus aureus, when injected subcutaneously in 

 suitable numbers, produces an acute local inflammation, which 

 is followed by suppuration, in the manner described above. 

 If a large dose is injected, the cocci may enter the blood stream 

 in sufficient numbers to cause secondary suppurative foci in 

 internal organs (cf. intravenous injection). 



