156 Regulation of Size in Unicellular Organisms 



generations of trypanosomes but throughout several 

 passages into new rats. The observations were con- 

 tinued through twenty passages, and it was found that 

 gradually the size returned to normal. Taliaferro ('24) 

 found the influences upon the parasites of the same 

 host at different ages of infection to change markedly 

 with time; the effects of different host species required 

 to be reinvestigated with this in mind. The changes of 

 size observed might be considered as the resultant of 

 continuation of growth during inhibition of multipli- 

 cation and vice versa. 



Wendelstadt and Fellmer also passed Trypanosoma 

 brucei from rats into tortoises, lizards, salamanders, 

 beetles, and slugs. In several of these species the try- 

 panosomes could not be found, but when the blood was 

 inoculated into new rats trypanosomes, sometimes of 

 immensely modified sizes, reappeared. Similar results 

 were in several instances found with Trypanosoma 

 lewisi. 



The species Trypanosoma rotatorium showed ana- 

 logous changes of size when Noller ('13) inoculated it 

 into tadpoles and frogs. Moreover, the sizes were tre- 

 mendously greater in the tadpoles than in the frogs, 

 so that if a tadpole bearing the parasites underwent 

 metamorphosis, its trypanosomes would become much 

 smaller. Various factors were investigated by Noller 

 to account for the size diversity, without finding a 

 crucial one. 



It may be pointed out that the diversities of sizes 

 among populations of trypanosomes which are derived 

 from different hosts, as in the observations of Bruce 

 ('11, '13), are completely paralleled by the diversities 

 of size in clones of protozoa at different ages of the 

 culture, or at different temperatures, or on different 

 foods. Yet Pearson ('14) postulated, from the prem- 

 ises of statistical significance, that in a particular in- 



