STATIONARY PHASE 95 



(2) With a large inoculum the M-concentration is reached rapidly, with a 

 small inoculum more. slowly. 



(3) Living bacteria introduced into fresh broth in M-concentration are unable 

 to multiply. 



(4) Living bacteria introduced into fresh broth in a concentration greater 

 than M die off until the M-concentration is reached. 



(5) If a culture that has reached its M-concentration is centrifuged and then 

 re-incubated, fresh growth will occur in the clear supernatant fluid till the M-con- 

 centration is reached. If, however, after centrifuging, the deposit is shaken up 

 so that the organisms are distributed once more throughout the medium, no growth 

 will occur. This seems to show that renewed growth is dependent not on the total 

 number of bacteria in a given volume of medium, but on their mode of distribution 

 within the medium. 



(6) If a culture that has reached its M-concentration is heated to 55° C. for a 

 time sufficient to destroy the majority but not all of the living bacteria, and is 

 then re-incubated, fresh growth will occur till the M-concentration is again reached. 

 This seems to indicate that' heat-killed bacteria do not appreciably interfere with 

 the biological space available. 



(7) Ordinary meat broth can be diluted 25 times or more without affecting 

 the level of the M-concentration, showing that it is not due to exhaustion of the 

 medium that growth ceases. In the diluted broth the turbidity, i.e. the total 

 count, is much less, but the number of living bacteria, i.e. the M-concentration, 

 is the same as in the undiluted broth. 



(8) The addition of an enriching substance, such as glucose, to the broth increases 

 the total number of bacteria produced, but the M-concentration of viable organisms 

 remains unchanged. 



(9) Growth does not cease with the attainment of the M-concentration ; fresh 

 organisms continue to be produced, but an equivalent number die off so that 

 the M- value remains constant. 



Many of these findings were confirmed by Fukuda (1929). This worker, how- 

 ever, pointed out that some of them, particularly Nos. 5, 7 and 8, held true only 

 with certain organisms. He found moreover that, if broth cultures ofPs. pyocyanea 

 were sterilized by heat and re-inoculated with fresh organisms, growth occurred 

 till the original M-concentration was reached. This experiment could be repeated 

 two or three times on the same culture, though with Saltn. gallinarum only one 

 quarter of the M-concentration was reached after the first heating. 



von WikuUil (1932) brought further evidence in support of Bail's hypothesis. 

 He found that, if two organisms A and B, each having the same M-concentration 

 of 1,600 million per ml., were inoculated simultaneously in the same numbers 

 into a tube of broth, the final M-concentration of the mixed culture was still only 

 1,600 million per ml., organism A constituting 800 million and organism B 800 

 million. The total physical space available had now to be shared between the 

 two organisms. If two organisms, A and C, having respective M-concentrations 

 of 1,600 million and 300 million per ml., were inoculated simultaneously into the 

 same tube of broth the final M-concentration was again 1,600 million per ml, 

 but this time the whole viable population consisted of organism A, The apparent 

 explanation was that A grew more rapidly than C, and so monopolized the available 

 space. 



Bail and his followers were more interested in making observations than in 



