132 Regulation of Size in Unicellular Organisms 



food is an important factor in controlling the sizes of 

 unicellular individuals. 



The influence of starvation has been investigated, 

 but rarely under well-controlled conditions. With most 

 mass-culture methods it is impossible to distinguish 

 lack of food from other influences such as progressive 

 chemical changes in the medium. Only where nutri- 

 ment is furnished either in the form of pure cultures of 

 visible organisms or as known concentrations of dis- 

 solved substances, or where all nutriment is suddenly 

 removed and sterile distilled water is substituted, can 

 effects be evaluated. 



It has been abundantly proven, 1 at least qualitative- 

 ly, in spite of inadequately controlled cultural condi- 

 tions, that starvation caused a tremendous reduction 

 of size of Paramecia, and particularly in breadth. Thus 

 in two experiments in Jennings's clone D, starvation 

 lasting seven days gave individuals with only 37 per- 

 cent of the original body volume on the average, and 

 starvation lasting eleven days gave individuals with 

 only 29 percent. Refeeding in the first case for only 

 24 hours gave recovery to 92 percent of the original 

 volume. What Jennings designated as starvation was, 

 of course, complicated by other cultural conditions. 



Similar reductions of size occurring under what were 

 termed conditions of starvation have been noted in 

 numerous species by many investigators, notably in 

 Stentor by Sosnowski ('99) and Allescher ('12), and 

 in Arcella by Hegner ('19b). 



With the older methods of culture, starvation must 

 have prevailed as often when it was unsuspected as 

 when it was known to be present. 



Total starvation. Colpidium was found by Wallen- 

 gren ('02) to respond to complete lack of food by a 



'Kazanzeff ('01), Wallengren ('02), Jennings ('08), Chainsky ('10), 

 Lipska ('10), Allescher ('12). 



