EXPERIMENTAL INOCULATION 209 



through the whole substance of the medium. On potatoes the growth is 

 an abundant reddish-brown layer resembling that of the glanders bacillus, 

 and the potato sometimes shows a greenish discoloration. 



From the cultures there can be extracted by chloroform a coloured 

 body, pyocyanin, which 

 belongs to the aromatic 

 series, and crystallises in 

 the form of long, deli- 

 cate bluish-green needles. 

 On the addition of a weak 

 acid its colour changes to 

 a red. 



This organism has dis- 

 tinct pathogenic action in 

 certain animals. Subcuta- 

 neous injection of small 

 doses in rabbits may pro- 

 duce a local suppuration, 

 but if the dose be large, 

 spreading hsemorrhagic 

 oedema results, which may 

 be attended by septicemia. 

 Intravenous injection may 

 produce, according to the 

 dose, rapid septicaemia with 

 nephritis, or sometimes a 

 more chronic condition of 

 wasting attended by albu- 

 minuria. 



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 awreus, when injected mbcutaneously 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). 



Intravenous injection in rabbits, for example, produces in- 

 teresting results, which vary according to the quantity used. If 



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