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Scientific Proceedings (127) 



culture, and variability in size, particularly the bimodality of 

 the frequency curves in the early stages of growth. Further 

 observations of this organism, varying the number and age of 

 the cells in the inoculum showed that these changes are constant 

 but vary in degree, the increase in size, and variation in size, 

 and the tendency to bimodality being greater with smaller and 

 older seedings; and that, while these changes take place during 

 the vegative phase of the culture, there is apparently no actual 

 correlation between the variations in size and the rate of cell 

 division. It is noteworty that the coefficient of variation in- 

 creases and decreases with the size of the cells. 



I have made a similar study of a chromogenic diptheroid 

 bacillus isolated from lake water. It is larger than most mem- 

 bers of this group of bacteria, but like the rest of the group de- 

 creases in size during the vegetative stages of growth and in- 

 creases during the resting period ; the curve for size is therefore 

 just the reverse of that for B. megatherium. The decrease in 

 size began after a latent period and during the logarithmic 

 growth phase. As the cells decreased in size the frequency 

 curves became more symmetrical and the variation decreased; 

 as the size increased again the curves became more extended 

 and showed skewness. There was no tendency to bimodality. 

 the single mode gradually shifting. The coefficient of variation 

 decreased with the actual decrease in size, i.e., during the period 

 of most rapid cell divisions. Therefore the coefficient of varia- 

 tion cannot be used as an index of rate of reproduction with 

 organisms such as these, where the entire population is subject 

 to fluctuations in size independent of the growth of the indi- 

 viduals from youth to maturity. The numbers of metachromatic 

 granules also decrease during the period of active growth and 

 increase during the resting period, and there is a positive cor- 

 relation between the size of the cells and the numbers of gran- 

 ules. But the num'ber of granules decrease more rapidly and 

 extensively than the size of the cells, and therefore the coeffi- 

 cient of correlation is high during the resting phase and low 

 during the vegetative phase. 



