138 Regulation of Size in Unicellular Organisms 



in size was similar to that during complete starvation 

 (figure 40 above), but was much slower. 



Heliozoa. As long as unknown food was used as 

 nutriment for protozoa, no distinction could be made 

 between the nutritional factor and other properties of 



42 



£40 



38 



JO 36 

 +-» 



C 

 ^J4 



o 32 



m 



30 









10 



2 4 6 8 



/Age of culture in days 



12 14 



Figure 42. Effect of age of culture upon mean body length in Colpoda 

 steinii. The progressions in two different cultures are represented. (Data 

 of Enriques, '09). 



the medium. It is now known that most unicellular 

 organisms create in culture fluid substances which are 

 detrimental to their further multiplication. Organ- 

 isms supplied with visible food, such as green organ- 

 isms raised on inorganic salts plus light, can have their 

 food supply accurately controlled independently of 

 other chemical factors. When there is no lack of food, 



