RATE OF GROWTH OF BACTERIA 43 



stress upon the fact that the lag period is shortened by increasing 

 the size of the seeding, and assumes that this is due to a mutual 

 stimulation of the cells by each other. Since the cells are separate, 

 this can only be accomplished by their shedding something into 

 the medium, and this, Robertson states, is a catalytic agent liberated 

 during the process of cell division. This mutual stimulation of the 

 cells Robertson refers to as the "allelocatalytic effect." 



But Cutler and Crump, and Greenleaf, failed to observe any 

 allelocatalytic effect with protozoa, and Peskett had similar negative 

 results with yeasts. Curran failed to observe any shortening of lag 

 when bacteria were seeded into broth separated from an actively 

 growing culture by a collodion membrane; therefore if there is an 

 extracellular catalyst it is not diffusible. But, as was demonstrated 

 by Chesney, there is no lag if the organisms are taken from a culture 

 in the maximum growth phase, and this was found to be true regard- 

 less of the size of the seeding by Sherman and Albus (1924b), 

 growth continuing at a maximum rate if the inoculum was but one 

 cell per c.c. It would seem, therefore, that if lag is due to the 

 lack of some extracellular catalyst, this catalyst is required only 

 by cells which had passed the logarithmic growth phase in the 

 preceding culture. As will be pointed out later, the effect of the 

 size of the seeding can be readily explained on the basis of variability 

 in the inoculated cells with regard to their ability to grow^ the 

 larger the number introduced, the greater the chance for obtaining 

 rapidly growing individuals. 



Since actively growing cells show no lag and cells taken from 

 a culture which has stopped growing do, Chesney rightly concluded 

 that the cause of the lag is to be found notin the medium, but in 

 the cells, and seeks this cause in an injury which the cells have 

 sustained in the preceding medium, and from which they must 

 recover before they can start to grow. He believes the cause of 

 this injury to be the toxic substance above mentioned. But proof 

 of the general existence of such a toxic substance has so far not 

 been furnished. However, this theory will still hold if we believe 

 that the cessation of growth is due to a lack of nutrients, and 

 that the cells have been injured by starvation. It would seem, at 

 least, that whatever causes a slowing and final cessation of growth 



