External Factors and Size 145 



tion in the "lag" period of multiplication; but body 

 growth of individuals was fastest when reproduction 

 was fastest. There was a lag in the accumulation of 

 total bulk as well as of numbers of individuals. 



Figure 47 shows that the maintenance of a large 

 size was very transient, as in B. megatherium. Trans- 

 fer to new medium at the end of each four hours would 

 keep the body length above 8 micra, but by the end of 

 six hours the body size would have to start enlarging 

 all over again. Henrici ('24a) showed that the amount 

 of inoculum had a large influence upon size attained. 

 It is possible that a very few individuals, preferably of 

 a motile species, in a large volume of medium, would 

 be able to maintain the maximum size and maximum 

 reproductive rate for many hours as has been shown to 

 hold true for yeasts and ciliates. 



Henrici ('24b) investigated the effect of concentra- 

 tion of organic nutrients upon body size, with the re- 

 sult shown in figure 48. More food material had rela- 

 tively little effect upon body size, though it had a 

 marked effect in prolonging the period of maximal re- 

 productive rate. 



Henrici ('28) formulated evidence contrary to the 

 possibility that "metabolic products" accumulate to 

 the point of beginning to inhibit growth and reproduc- 

 tion, and suggested that internal changes ("physio- 

 logical youth") were induced by the mere presence of 

 fresh medium. The suggestion was made that the fac- 

 tor of cell size which varied may be the surface tension 

 at its boundaries, this being dependent in some way 

 upon influences of the medium upon metabolism or 

 chemical constitution. 



Henrici ('28) presented a considerable amount of 

 data illustrating the effects of various properties of 

 culture fluid upon several species of bacteria. Par- 

 ticularly in relation to variability of size at different 



