Rates of Growth of Individuals 37 



first sixty minutes of the growth cycle the starved in- 

 dividuals underwent the same changes of size as the 

 controls. But in these cases the controls also exhibited 

 increases only of length, and no increases of volume. 

 At 5 hours and at 24 hours the starved organisms were 

 far behind the controls with respect to volume; yet 

 they too had gained. As far as the data are depend- 

 able, it must be true that volume may increase for at 

 least 24 hours in the absence of food. But it is more 

 likely that small amounts of food were available. 

 Otherwise volume must have increased by the incor- 

 poration of water; possibly accompanied by the gain, 

 through processes other than alimentary, of certain 

 dissolved substances. 



That growth of individuals may occur by mere 

 changes of relative water content is supported by the 

 evidence regarding Bacillus coli already discussed in 

 connection with figure 2 and with table 3. Perhaps 

 most striking of all the changes of water content are 

 the decreases of volume just before fission shown by 

 the data of Jennings ('08b) in figure 6. Whereas it is 

 possible that this shrinkage was due to some sort of 

 defecation preparatory to fission, there were no obser- 

 vations to support the possibility. 



Is the rate of growth limited only by nutritive ac- 

 quirement? This question has not been asked fre- 

 quently enough; probably because no case is possible 

 in which rapid and continued growth can occur with- 

 out assimilation of something. But in many organ- 

 isms, as in an adult man, it may be seen clearly that 

 assimilation can proceed without growth resulting. 

 Upon unicellular organisms the data are insufficient to 

 decide; but the shape of the growth curve of Jennings 

 seems to indicate that increase of size is not propor- 

 tional to food acquirement, even allowing for the pos- 

 sibly greater speed of digestion and of ejection of fluid 



