BIOLOGY OF PNEUMOCOCCUS 41 



lation, under certain cultural conditions, of peroxide in the me- 

 dium. Hager,* by daily neutralizing the newly formed acid has 

 succeeded in prolonging the period of growth and, therefore, in ob- 

 taining unusually heavy yields of pneumococci from a single lot of 

 broth. 



Felton and Dougherty 423 " 4 contrived an ingenious apparatus for 

 delivering a continuous supply of pneumococci at the stage of most 

 active growth. By an automatic device, an inoculum of vigorous, 

 young culture was removed from the exhausted medium and 

 planted in a flask containing a fresh food supply of milk. The 

 transfers were made at two, four, and eight-hour intervals. Propa- 

 gation by this method at eight-hour intervals raised the virulence 

 of the strain to a degree unprecedented in any former in vitro ex- 

 periments. Methods for obtaining large amounts of living pneu- 

 mococci for chemical study as well as for other purposes have 

 been described by Felton and Huntoon, 667 while that of Hager has 

 not yet come to publication. f 



These media, varying in their constituents, all require heavy 

 inoculation with a vigorous culture (Gillespie 515 ), careful initial 

 adjustment or subsequent correction of the reaction and, of 

 course, incubation at a constant temperature of about 37.5° if 

 they are to give a large yield. Dubos 331 explained the necessity for 

 large amounts of inoculum in seeding broth as being based on the 

 establishment of a proper reduction potential in the medium. This 

 condition is brought about by the large inoculum owing to the re- 

 ducing properties of the bacterial cells. 



ACCESSORY SUBSTANCES 



Optimal growth conditions, that is, as far as rate of growth, 

 number, and viability of the organisms are concerned, can be pro- 

 vided beyond those already mentioned by the addition of a variety 

 of substances. Autoclaved gelatin, by its buffering action in addi- 

 tion to its nutritive elements, has been found by Piatt 1096 to induce 



* Personal communication. t See Appendix. 



