THE LAG PHASE 87 



tion of meningococci by normal serum, Gillespie (1914) on the salt agglutination of 

 pneumococci, and Sherman and Albus (1923) on the acid agglutination of Bact. 

 coli, all suggest that young cells are less susceptible than old to non-specific 

 agglutination. This presumably is due to an alteration in the electric charge or 

 to some other change on the surface of the cells. 



Summarizing the data yielded by these observations, we see that during the lag 

 phase of growth there is a progressive enlargement of the cells before division 

 occurs, associated with a rapid increase in their metabolic activity and their 

 susceptibility to heat and disinfectants. Before a cell can divide, it must increase 

 in size. The so-called lag phase of growth seems to be occupied mainly by this 

 process of cell enlargement. Up to this point all recent workers are in agreement. 

 On two subjects, however, there is some discrepancy of opinion. Firstly, do all 

 cells, when inoculated into a fresh medium, begin to grow at once ? In other words, 

 is there no such thing as a true lag phase ? It is a little difficult to answer this 

 question, but the available evidence suggests fairly strongly that under certain 

 conditions cells introduced into a fresh medium take some time to adjust them- 

 selves to the new conditions before they start to grow, even in size. The duration 

 of this " phase of adjustment " varies with the conditions. While it lasts, it con- 

 stitutes a true lag phase. If the organisms in the inoculum are vigorous and 

 unharmed and the medium into which they are introduced is favourable, cell 

 enlargement may occur at once, and no true lag phase will be seen. If, on the 

 other hand, they are suffering, from the toxic effects of their previous environment, 

 or the medium into which they are inoculated has an unfavourable pH or salt 

 content, then some time may elapse before cell enlargement begins. 



Secondly, are we justified in referring to the orderly change that occurs in the 

 enlargement and division of a bacterial cell as a life-cycle ? Apart from mere 

 difference of opinion on the advisability of using such a term, the answer must 

 depend on whether there is a real differentiation of morphology and function at 

 different stages of growth. The observations of Henrici (1928), in particular, 

 leave no doubt about the differences in size, structure, and staining affinity of 

 bacterial cells at different stages of growth, but the evidence in regard to their 

 metabolic activity is a little conflicting. Hershey (1939), for instance, maintains 

 that the metabolic activity is the same for cells at all stages of growth, provided 

 that it is expressed in terms of amount of bacterial protoplasm rather than in 

 terms of individual cells. It is true that in absolute values a cell in the late lag or 

 early logarithmic phase uses more oxygen and produces more COj than a ceil in the 

 stationary or decline phase, but this, according to Hershey, is merely due to a 

 difference in size of the cells. The respiration of any unit amount of protoplasm is 

 the same with cells at all stages of growth. Huntington and Winslow (1937) and 

 Winslow and Walker (1939), however, do not agree with this view. They found 

 that the rate of CO2 production per cubic micron of bacterial substance was much 

 higher during the lag and early logarithmic phases than during the stationary phase. 

 They believe, therefore, that young protoplasm is characterized by a greater rate 

 of metabolism, and that the use of such a term as life-cycle for bacteria is justifiable. 

 Further evidence is required to settle this important difference of fact. 



If we accept the view of Winslow and Walker, we shall summarize as follows : 



On the ground (a) that newly generated bacilli in the logarithmic phase, when 

 transferred to a fresh medium, start multiplying without exhibiting any lag phase ; 

 (6) that bacilli from cultures in all other stages show a lag phase before they start 



