74 BIOLOGY OF PNEUMOCOCCUS 



the occasional cases of pneumonia which show a decrease in the 

 oxygen capacity of the blood, the decrease is probably due to the 

 formation of methemoglobin. The latter is removed from the circu- 

 lation, however, as rapidly as it is formed, so that it can seldom be 

 detected even qualitatively, and is probably never the cause of 

 cyanosis." The practical impossibility of demonstrating methemo- 

 globin in the circulating blood was also experienced by Schnabel. 1233 

 The explanation of the phenomenon of methemoglobin produc- 

 tion is of importance not only in so far as this special reaction is 

 concerned, but also because it suggests a mechanism by which 

 pathological effects may be produced by bacteria which appar- 

 ently elaborate no soluble toxin. 



PEROXIDE FORMATION 



The work of McLeod and Govenlock, 885 of McLeod and Gor- 

 don, 881 " 3 and of McLeod, Gordon, and Pyrah 884 was confirmatory 

 of Cole's results and amplified our knowledge of the property pos- 

 sessed by pneumococci to form peroxide during growth. The au- 

 thors ascribed the greenish or yellowish discoloration produced 

 on heated blood media to an accumulation of peroxide, showed that 

 the death of pneumococci in cultures was brought about by an ex- 

 cess of the same product, and demonstrated that the substance was 

 not organic peroxide but hydrogen peroxide. It was not formed in 

 cultures deprived of oxygen, nor in cultures that contained abun- 

 dant catalase. 



Penfold 1077 disclosed another manifestation of the oxidizing ac- 

 tion of pneumococci. According to him, all pneumococci and prob- 

 ably all streptococci acting on certain aromatic amines, notably 

 aniline, benzidine, and the toluidines, produce pigment. When 

 pneumococcal and streptococcal cultures were grown on citrated 

 horse-blood agar containing benzidine, the colonies appeared black 

 by transmitted light and metallic blue by reflected light with dark 

 discoloration extending far into the medium around the colony. 

 This pigment production from the amines is a peculiarity shared 



