EXPERIMENTAL INOCULATION 181 



in the form of long, delicate bluish-green needles. On the addition of 

 a weak acid its colour changes to a red. 



This organism has distinct pathogenic action in certain animals. 

 Subcutaneous injection of small doses in rabbits may produce a local 

 suppuration, but if the dose be large, spreading haemorrhagic oedema 

 results, which may be attended by septicaemia. Intravenous injection 

 may produce, according to the dose, rapid septicaemia with nephritis, or 

 sometimes a more chronic condition of wasting attended by albuminuria. 



Micrococcus tetragenus. 

 This organism, first de- 

 scribed by Gaffky, is char- 

 acterised by the fact that it 

 divides in two planes at right 

 angles to one another (Fig. + fe 

 57), and is thus generally *J " * * 1 



found in the tissues in groups iJ _f * W 



of four or tetrads, which are '-. W * * * 



often seen to be surrounded ^ 



by a capsule. The cocci ; li 



measure 1 ^ in diameter. ! ^ M 



They stain readily with all 

 the ordinary stains, and also 

 retain the stain in Gram's 

 method. * 



It grows readily on all * tf> 



the media at the room tern- * $F * 



perature. In a puncture cul- 

 ture on peptone - gelatin a 



Cm/alollfthetrack'of "he F '- 57-Micrococcus tetragenus ; young 

 needle, whilst on the surface c ,..?^" S. ?. " 



- W ' 

 i * 



there is a thick rounded disc Stained with weak carbol-fuchsin. 

 of whitish colour. The gela- 

 tin is not liquefied. On the surface of agar and of potato the growth 

 is an abundant moist layer of the same colour. The growth on all 

 the media has a peculiar viscid or tenacious character, owing to the 

 gelatinous character of the sheaths of the cocci. 



White mice are exceedingly susceptible to this organism. Subcutaneous 

 injection is followed by a general septicaemia, the organism being found 

 in large numbers in the blood throughout the body. Guinea-pigs are 

 less susceptible ; sometimes only a local abscess with a good deal of 

 necrotic change results ; sometimes 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 



