External Factors and Size 157 



stance the chances were less than one in a hundred 

 thousand that two selected frequency curves of size 

 represented the same species of parasite in different 

 hosts. The biological responses to environments must 

 be taken into account more seriously than the differ- 

 ences which appear to exist in the "internal" differ- 

 entiation of unicellular individuals. 



Other parasite hosts. A number of parasite species 

 were inoculated by Hegner ('29) from the intestinal 

 tracts of various birds into the intestinal tracts of para- 

 site-free chicks. He measured the size frequencies when 

 in the original hosts, after the various inoculations, and 

 after cultivation on artificial media. Large differences 

 of mean sizes were found in each situation. The size 

 of the organism is, obviously, just as much a character- 

 istic of the medium in which it finds itself as of the species 

 to which it belongs. 



5. Radiations 



The studies of the effects of radiations upon size are at 

 present wholly inadequate and primitive. Pauli and 

 Hartmann ('24) observed that Paramecia swelled after 

 being treated with cathode rays. The treatment was 

 evidently severe, since new surfaces and new vacuoles 

 formed in the cytoplasm. Calkins ('29) measured a 

 sudden and large diminution in the size of Uroleptus 

 ten minutes after exposure to a mercury-vapor lamp. 

 After this shrinkage the organisms did not change in 

 volume, though it was 48 hours before death oc- 

 curred. For reproducible results monochromic radia- 

 tions of measured intensities must be used, and signifi- 

 cant numbers of organisms must be measured at vari- 

 ous periods of time after treatment has been adminis- 

 tered. 



