40 Regulation of Size in Unicellular Organisms 



ium chloride solutions were similarly complicated by 

 the use of tin-condensed distilled water which was 

 lethal. But a series of measurements was made upon 

 individuals in sodium chloride solutions containing 

 hay-infusion. Figure 18 shows that in these media in- 

 crease in body length occurred just as in the controls. 

 But after some time, namely, 40 minutes in 0.10 M 

 and 90 minutes in 0.05 M, sudden decreases occurred, 

 which were followed shortly by the death of some of 

 the individuals. Weaker solutions, though increasing 

 the osmotic pressure several fold, had no significant 

 effects. 



Temperature. Temperature, of course, affects 

 markedly the rate of growth. The data of Popoff ('08) 

 show this influence very clearly (figure 13), but he 

 made measurements at only two temperatures. 



A large series of different temperatures was studied 

 by Ward ('95) in relation to the growth of Bacillus 

 ramosus. In these filaments of bacteria he ignored 

 the partitioning into cells and simply found how long 

 it took for a given chain to double its length, and there- 

 fore its volume. The rhythms of increase in length, 

 shown in figure 16, were ironed out by the consider- 

 able periods of time which elapsed between measure- 

 ments ; and it has already been seen (figure 15) that the 

 increment is proportional to the time interval, regard- 

 less of the absolute length of the chain of bacilli. 



Ward's results, shown in figure 19, cover almost the 

 entire range of temperatures at which the bacilli live, 

 for above 39°C. they are killed. The relationship be- 

 tween temperature and rate of increase in volume is 

 not a logarithmic one, as can be supposed to be true in 

 the case of some temperature effects. 



If the volume of growing micro-organisms be taken 

 only once for each generation, then, of course, the rate 

 of growth is the same as the rate of fission, assuming 



