C.-E. A. WINSLOW 63 



the observation of Penfold (1914) that generation time decreases with an increase in 

 inoculum. Rettger (1918) suggests that lag in culture media may be decreased or 

 eliminated by supplying "satisfactory substitutes for the intermediate bodies in the 

 form of amino acids and perhaps amines of simple composition, and also certain 

 growth-accessory substances." 



3. THE PHASE OF INCREASE 



When the phase of adjustment (whether this involves selection of more readily 

 viable cells or the development within the cells of intermediate products favorable to 

 rapid growth, or both) has been completed in a favorable medium, there next follows 

 a period of rapid and regular increase. During this phase it has been shown by Clark 

 and Ruehl (1919) that the average size of cell is greatly increased as compared with 

 that which is dominant in an older culture. According to Henrici (1921, 1922, 1923, 

 1924), the large cells appear toward the end of the lag phase and the beginning of the 

 phase of logarithmic increase, the average size returning to normal as the phase of in- 

 crease proceeds. In a highly unfavorable medium, this phase will of course be entirely 

 suppressed; but it is a very common phenomenon, by no means limited to the rich 

 culture media of our laboratories. It was perhaps first exhaustively studied by the 

 early water bacteriologists in the case of samples of natural waters which had been 

 placed in a new environment by the mere fact that they had been collected in a sam- 

 ple bottle in the laboratory. Thus Leone as early as 1886 records the following results 

 for Munich water simply stored in flasks without the addition of any foreign material : 



Storage Period in Days Numbers per Cc 



o 5 



1 100 



2 10 , 500 



3 67,000 



4 315,000 



5 Over 500 , 000 



Miquel (1891) gives the striking curves reproduced in Figure 2 for a series of spring 

 waters stored in flasks at 29°-3o° C. 



In the phase of logarithmic increase we are dealing with a very simple relationship 

 due to the fact that binary fission carried on at a regular rate leads to a progressive 

 logarithmic increase. In other words (Ledingham and Penfold, 1914) : 



t=K log b/B, 



when / = time, & = final number, and 5= initial number. 



The actual figures obtained for generation times under certain more or less typical 

 conditions are indicated in Table II. The studies of multiplication in soil, feces, and 

 bottled waters did not include counts made at sufficiently frequent intervals to be 

 quite certain that only the phase of logarithmic growth was included, but they are 

 cited in the table as representing the most rapid increases (under this condition) with 

 which the writer is familiar. 



It appears from all the more careful work upon this subject that under the most 



