BACTERIA AND DISEASE 299 



adoption of Marmorek's methods attempts have been made 

 to prepare an antitoxin. 



Streptococcus pyogenes has been isolated from the mem- 

 brane of diphtheria, and from small-pox, scarlet fever, vac- 

 cinia, and other diseases. In such cases it is not the causal 

 agent, but merely associated with the complications of these 

 diseases. Suppuration and erysipelas are the only patho- 

 logical conditions in which the causal agency of streptococ- 

 cus has been sufficiently established. 



3. The Bacillus pyocyaneus occurs in green pus, and is 

 the cause of that colouration. Gessard was the first to prove 

 its significance, and he describes two varieties. 



It is a minute, actively motile, non-sporulating bacillus, 

 which occasionally complicates suppuration and produces 



r.:< *H! 

 I? ** *l# 



MICROCOCCUS TETRAGONUS 



green pus. Oxygen is necessary for pigmentation, which is 

 due to two substances : pyocyanin, a greenish-blue product 

 extracted with chloroform, and pyoxanthose, a brown sub- 

 stance derived from the oxidation of the former pigment. 

 Both these colours are produced in cultivation outside the 

 body. On gelatine the colour is green, passing on to olive. 

 There is liquefaction. On potato we generally obtain a 

 brown growth (compare Bacillus coli, B. mallei, and others). 

 The organism grows rapidly on all the ordinary media, 

 which it has a tendency to colour throughout. 



It will be remembered that when speaking of the antagon- 

 ism of organisms, we referred to the inimical action of 

 Bacillus pyocyaneus upon anthrax. 



4. Micrococcus Tetragonus. This species occurs in phthisi- 



