128 Regulation of Size in Unicellular Organisms 



tion differ among diverse types of unicellular organ- 

 isms, some species may yet be found in which size in- 

 creases with temperature. 



2. Food 



Kinds of living food. Random observations have 

 frequently been made which indicate that qualitatively 

 different foods modify the characteristic body sizes of 

 bacteria and protozoa. Only those instances where 

 pure clones were present need be seriously considered. 

 Yet without this precaution the results of Maupas 

 ('88) are probably reliable. In Onychodromi which 

 were fed on "large infusoria" the mean body length 

 was 300 micra; fed on "small Cryptochila" the length 

 was 150 micra; the breadth being in proportion. In 

 Stylonychia when fed Cryptochila the mean length 

 was 160 micra, while when fed the bacteria of wheat 

 infusion it was 125 micra; and the fission rate was only 

 37 percent of that on the first food. Of course various 

 chemical conditions in addition to the food differed in 

 two such contrasting cultures. 



The heliozoan Actinophrys is markedly larger when 

 fed upon Gonium than when fed upon Chlorogonium 

 (Belar, '22). This difference is not entirely due to 

 larger or more numerous food vacuoles. 



Cutler and Crump ('27) observed that the soil rhizo- 

 pod Hartmanella undergoes fission at different sizes 

 when fed upon diverse species of bacteria. When feed- 

 ing on certain bacteria called YB, the mean volume 

 just before fission was said to be 274 cubic micra ; while 

 on bacteria SE it was 190 cubic micra. No idea can 

 be obtained how many measurements were made to ar- 

 rive at these values. 



Observations under highly controlled conditions 

 were made upon Colpoda (Adolph, '29). The ciliates 

 were in a uniform solution of very dilute inorganic 



