38 Regulation of Size in Unicellular Organisms 



from food vacuoles in the adults. It is usually assumed 

 that a Paramecium ingests its food at a fairly uniform 

 rate throughout the hours of its individual existence. 

 If so, the food certainly has not a uniform effect upon 

 the mass of the body. Thus far, at least, growth ap- 

 pears to depend not wholly upon the food supply. 



But there is evidence that food is not ingested at a 

 uniform rate throughout one generation's life. Lund 

 ('14) studied the ingestion of food particles in indi- 

 viduals of Bursaria which had been previously starved 

 for 24 hours. He found that those which were allowed 

 to feed for only five minutes ingested almost as many 

 particles as those of the same culture which were left 

 with the same food for one hour. Again, in Hartman- 

 ella starvation was found by Cutler and Crump ('27) 

 to result in a gradual decrease of body volume, as 

 shown in figure 14. But when food was again sup- 

 plied, the effect was tremendous as a result of the 

 previous 24 hours of starvation; the gain in bulk was 

 six times as great as in the control organisms fed con- 

 tinuously with the same food. Part of this might be 

 due to the inflation of true body-substance by food 

 vacuoles; but not nearly all of it could be such. If, 

 therefore, previous starvation modifies the rate of in- 

 gestion, it is misleading to leave out of account the 

 influences of age and other physiological stages upon 

 this rate. Fission might be considered as equivalent to 

 previous starvation, for it can be followed, though per- 

 haps not immediately (Estabrook), by a period of very 

 rapid assimilation. 



Chemical influences. The effects of chemical con- 

 ditions upon growth of individuals were studied by 

 Estabrook ('10) in Paramecium. He placed individ- 

 uals just after fission in solutions of various substan- 

 ces, chiefly alkaloids and sodium chloride. The effect 

 of the alkaloids was not marked except in those con- 



