C.-E. A. WINSLOW 6i 



was longer. In fresh unsterilized milk the lag lasted 6 hours, but was apparently abol- 

 ished by previous heating of the milk. Cohen and Clark (191 9) note that the onset of 

 the period of maximal increase for Bad. coli was 2-4 hours in peptone phosphate broth 

 atpH values between 6.1 and 8.1 but was increased to 3-5 hours at pH values below 

 5.5, and to 10-12 hours at pH 8.9 (37° C). 



A high temperature, of course, decreases the length of the phase of adjustment. 

 According to Whipple's data for water bacteria stored in sample bottles, the period of 

 lag averaged about 8 hours at 20^-24° C. and 17 hours at 12° C. Lane-Claypon (1909) 

 reports a lag period in culture media varying from i hour at 42° to 6 hours at 20° C. 



An extreme case of lag may probably be found in the fact that both spores and 

 vegetative cells occasionally show an exceedingly slow development in entirely favor- 

 able culture media. Thus Burke, Sprague, and Barnes inoculated broth and agar 

 tubes with approximately one cell of Bad. coli per tube. While 85 per cent of the 473 

 tubes which gave growth did so within 2 days and 97 per cent within 6 days, there 

 were 10 tubes which developed only on the fourteenth day, 4 only on the fifteenth, 

 and 4 only on the sixteenth. Spores of B. subtilis remained dormant under similar 

 conditions for 39 days and spores of B. megatherium for 90 days. 



The fundamental causes of the lag phenomenon have been exhaustively discussed, 

 particularly by Rahn (1906), Tenfold (1914), Chesney (1916), and Buchanan (1918). 

 The phenomenon must be considered in the light of the observation of Miiller (1895) 

 and Hehewerth 1901) that the rate of increase of bacteria in a given medium bears a 

 generally inverse relation to the age of the mother-culture from which this medium 

 was inoculated. Hehewerth found that the generation time for Bad, coli in broth, 

 when transferred from a young broth culture, was 21-27 minutes while when 

 transferred from an older broth culture it was 43 minutes. It is of cardinal sig- 

 nificance to note that lag disappears entirely if transfer is made to an identical medi- 

 um while the mother-culture is in its phase of logarithmic increase (Tenfold, Barber, 

 Chesney). Furthermore, Tenfold shows that if the growth in a culture be stopped by 

 chilling for a very short time the growth recommences at a normal rate when the tem- 

 perature is raised; while more prolonged chilling and subsequent increase of tempera- 

 ture is followed by a lag. 



The occurrence of lag cannot in general be due to the presence of inhibitory sub- 

 stances carried over from the mother-culture (as might be concluded from Tenfold's 

 finding that centrifugalized cultures showed decreased lag) since we note the same 

 phenomenon in a sample of water transferred from a lake to a sample bottle. Further- 

 more, Tenfold and Chesney show that lag in a secondary culture does not increase 

 with the progress in the mother-culture of the logarithmic phase, and that while it 

 does grow more marked with passage from the logarithmic phase to the phase of 

 crisis there is no further increase with later aging of the mother-culture. 



Lag is therefore primarily associated with the biological condition of the cells 

 which are transferred to a new medium (or placed under new environmental condi- 

 tions, as when a water sample is collected). Under certain conditions this may be as- 

 sociated with definite prior injury to the cells. Sturges (19 19) found that the develop- 

 ment of colonies on plates seeded from sewage disinfected with copper or sulphurous 

 acid was very much retarded (although the fact that chlorine-disinfected sewage ex- 



