40 BIOLOGY OF PNEUMOCOCCUS 



pensions of washed pneumococci dissolution is most marked within 

 the range pH 5.0 to 6.0. Some disintegration occurs toward the 

 alkaline side but none at the most acidic end of the scale. 



For the successful initiation of growth in broth, once a pure cul- 

 ture is obtained, a fairly heavy amount of inoculum is advisable. 

 Cole used 0.1 cubic centimeter for every cubic centimeter of broth. 

 These amounts are obviously impossible when cultures are to be 

 planted from single colonies or from mouse-hearts' blood and simi- 

 lar materials. When original infectious material is used as inocu- 

 lum a small amount usually suffices. A generous planting, however, 

 favors multiplication. 



The cycle of pneumococcal growth in broth has been studied by 

 Chesney. 220 When broth is inoculated with a culture that has passed 

 the stage of maximal growth, there ensues a latent period before 

 growth appears in the freshly seeded broth. When, however, inocu- 

 lation is performed with cultures at their maximal rate of growth, 

 there is no delay in multiplication. This initial latent period or 

 lag — that is, the interval between the time of seeding and the time 

 at which maximal rate of growth begins — is followed by a phase of 

 rapid growth, during which the organisms are dividing regularly. 

 This stage is followed by a stationary period, in which the organ- 

 isms cease to multiply at maximal rate so that the increase in 

 number becomes slower and finally ceases and, although they re- 

 main viable, the number of cells present in a unit volume remains 

 approximately constant for an appreciable length of time. Finally 

 the period of decline sets in, in which the number of living organ- 

 isms begins to decrease. Chesney believed that this lag is an expres- 

 sion of injury which the bacterial cell sustains from previous envi- 

 ronment. 



The failure of pneumococci to continue to grow and multiply 

 after the stationary period is due to the production of acid or pos- 

 sibly of other inhibiting substances. Morgan and Avery 915 listed 

 the inhibiting factors as the accumulation of acid products, the 

 exhaustion of nutritive substances, and the formation and accumu- 



