EXPERIMENTAL INOCULATION 209 



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 alliuminuria. 



Micrococcus tetragenus. This organism, first described by Galfky, is 

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

 one another (Fig. 55), and is 

 thus generally found in the 

 tissues in groups of four, or 

 tetrads, which are often seen 

 to be surrounded by a cap- 

 sule. The cocci measure 1/4 f ^|> 

 in diameter. They stain J 

 readily with all the ordinary C 



stains, and also retain tin.- 

 stain in Gram's method. ^ * . 



It grows readily on all the I ^ ^ 1 



media at the room tempera- f 

 ture. In a puncture culture 



on peptone-gelatin a pretty J -. 



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 liquefied. On the sur- 

 face of a^ar and of potato *- 5o. Micrococcus tetragenus ; young 



culture on agar, showing tetrads. 

 Staged with weatca r bol.f,,ch si ,, x ,000. 





 t 

 . 



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, 

 an these have been most fully studii-d. 



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 pyogenr-. 



