134 PROTOZOOLOGY 



Hirshfield (1951) subjected Amoeba proteus to ultraviolet radiation 

 and noticed that irradiation of the whole and nucleated half amoebae 

 delays division immediately following exposure; later progeny of the 

 irradiated amoebae have a normal division rate; amputation of half 

 of the cytoplasm greatly increases the radiation sensitivity as meas- 

 ured by delayed division or by the dose required for permanent in- 

 hibition of division (sterilization dose) ; individuals that have re- 

 ceived this dose may survive for 20-30 days; and the survival time 

 of an enucleate fragment is very much reduced by small (200-500 

 ergs/sq. mm) doses. The two workers consider that the overall radia- 

 tion effect may have both nuclear and cytoplasmic components. By 

 exposing Pelomyxa carolinensis to 2537 A ultraviolet irradiation, 

 Wilber and Slane (1951) found the effects variable; however, all re- 

 covered from a two minutes' exposure, none survived a 10-minute 

 exposure, and 70 per cent of fat were released after two minutes' 

 exposure. 



Zuelzer (1905) found the effect of radium rays upon various Pro- 

 tozoa vary; in all cases, a long exposure was fatal to Protozoa, the 

 first effect of exposure being shown by accelerated movement. Hal- 

 berstaedter and Luntz (1929, 1930) studied injuries and death of 

 Eudorina elegans by exposure to radium rays. Entamoeba histolytica 

 in culture when subjected to radium rays, Nasset and Kofoid (1928) 

 noticed the following changes: the division rate rose two to four 

 times by the exposure, which effect continued for not more than 24 

 hours after the removal of the radium and was followed by a re- 

 tardation of the rate; radium exposure produced changes in nuclear 

 structure, increase in size, enucleation or autotomy, which were more 

 striking when a larger amount of radium was used for a short time 

 than a smaller amount acting on for a long time; and the effects 

 persisted for four to six days after the removal of the radium and 

 then the culture gradually returned to normalcy. Halberstaedter 

 (1914) reported that when exposed to Beta rays, Trypanosoma 

 brucei lost its infectivity, though remained alive. 



Halberstaedter (1938) exposed Trypanosoma gambiense to X-rays 

 and found that 12,000r rendered the organisms not infectious for 

 mice, while 600,000r was needed to kill the flagellates. Emmett 

 (1950) exposed T. cruzi to X-rays and noticed that dosages between 

 51,000r and 100,000r were necessary to destroy the infectivity of this 

 trypanosome; the cultures, after exposure to 100,000r, appeared to 

 be thriving up to three months; and the effects of exposure were not 

 passed on to new generations. 



When Paramecium bursaria were exposed to X-rays, Wichterman 



