24 MORPHOLOGIC VARIATION 



than in cultures grown at a higher temperature; the death rate is 

 also correspondingly slower at lower temperatures. This was not 

 confirmed by Tanner and Wallace with thermophiles. 



Of the various factors which influence the rate of growth and 

 the form of the growth curve, the initial number of cells introduced 

 into a unit volume of medium seems to be one of the most important. 

 Rahn first showed that the duration of the lag phase was greater 

 with smaller seedings, and Penfold, although finding fault with Rahn's 

 data, was able to confirm his conclusion. Montank has demonstrated 

 the same thing for yeasts (Figure 3). It should be noted that the 

 occurrence of a lag phase depends upon the age of the culture used 

 for seeding, and that if the material used for inoculation is in the 

 active growth phase no lag will occur in the subculture no matter 

 how small the seeding (Sherman and Albus, 1926). 



McKendrick and Pai noted that the final yield in cultures fourteen 

 hours old was practically independent of the size of the seeding, 

 and that therefore the rate of growth is higher for smaller seedings. 

 This was confirmed by Graham-Smith as long as the seedings are 

 smaller than the normal maximum yield of the medium. Adrian 

 Brown has calculated the mean rates of growth of yeast cultures 

 with various sized seedings, and derived a simple formula to express 

 the relationship. Figure 2 is a curve plotted from his data, in which 

 the yield from one cell in eighteen hours is plotted against the mitial 

 density of the population. It will be seen that the curve is hyper- 

 bolic, and that with very small seedings a very slight difference 

 in the number of cells introduced makes a very great difference in 

 the rate of grow^th, while with larger seedings the effect is slight. 

 In these observations only the mean rate of growth for relatively 

 long periods is available, i.e., it is impossible to separate the effects 

 upon the lag phase and the growth phase. 



Montank, working in my laboratory, has, however, obtained data 

 in which such a separation is possible.* His results are shown graphi- 

 cally in Figure 3, the data for which are presented in Table I. In 



*I am greatly indebted to Mr. Montank for the privilege of using here 

 his as yet unpublished observations, part of an investigation still in progress. 

 The data from which his curves have been plotted will be found in Tables 1 

 and 2. 



