BIOLOGY OF PNEUMOCOCCUS 43 



tral dyes. They were variable in size and had fairly regular out- 

 lines and a granular structure. Inasmuch as these bodies did not 

 appear in serum media previously heated at 56° for one-half hour, 

 but did appear when the temperature was no higher than 50°, 

 Bordet thought that their production was due to alexin, although 

 they were not present in broth containing serum from rabbits vac- 

 cinated against Pneumococcus, either of homologous or heterolo- 

 gous type. 



Blood and serum, in addition to contributing some nutritive 

 substances, act as buffers in controlling the reaction and, being 

 colloids, arrest any toxic action of inorganic salts. Blood, because 

 of its oxidation-reduction system, tends to maintain a proper oxy- 

 gen balance, while the iron in the hemoglobin seems to act as a 

 catalase. In studying the supposed necessity for hemoglobin for 

 the growth of Bacillus influenzae, Thjotta 1301 discovered that this 

 substance could be omitted if extracts of mucoid bacilli or of Ba- 

 cillus proteus were substituted. Thjotta looked upon the accessory 

 substance in such extracts as a vitamin which, in many ways, cor- 

 responded to Wildier's "Bios" of yeast, the "auxomones" of Bot- 

 tomly, or the hormones. Then Thjotta and Avery 1392 " 3 learnt that 

 these substances — the "V" factor — alone would not support the 

 growth of hemophilic bacteria through several generations, but 

 that another substance, the so-called "X" factor, contained in red 

 corpuscles was essential. This X factor is heat-stable and acts in 

 minute amounts. Both the V and X factors are required for the 

 continued and complete development of Pneumococcus as well as 

 for the growth of hemophilic organisms. 



Baudisch and Dubos 89 investigated the influence of iron com- 

 pounds on the viability of pneumococci. Small amounts of iron 

 oxide prolong the life of avirulent strains but are less favorable to 

 virulent strains. Iron may be stimulating or harmful depending 

 upon the particular chemical radical with which it is combined. 



Another accessory substance of animal origin, recommended by 

 Quiroga, 1115 is liver. The addition of an extract of beef liver to 



