316 UADIATION HI()I,(»(;V 



tozoan Colpoda steinii is under excelleiil experimental control. Exposure 

 to a special medium results in complete excystment, startinji; at alxjut 2 hr 

 after exposure and endinji" in less than I hr from its inception. Taylor el 

 al. (193()) huve shown tiiat a dose of 88, 100 i- of X rays fj;i\'(>n at the rate of 

 1280 r/'sec within the first (iO min after exposure of the ciliates to the 

 excystment medium increases the time to 50 per cent excystment to about 

 420 mill. The same dose given 120 min after exposure to the excystment 

 medium has very little effect. From the form of the curves of percentage 

 excj'sted against time, it is concluded that, in the period between GO and 

 120 min, there is a mixture of sensitive and resistant cysts and some in a 

 transitional state between sensitive and resistant. The cysts in this 

 transitional state are apparently moi'e easily prevented from excysting by 

 the X rays than are cysts in the; other two states. 



Giese (1938a, 1941, 1945a), using the same techniques, has shown thai 

 monochromatic ultraviolet also increases the time to excystment. The 

 action spectrum has been determined for wave lengths from 2537 to 3()()() 

 A. There is a small peak at 2804 A suggestive of the absorption spectrum 

 of certain proteins. The dose of 2654 A ultraviolet to double excystment 

 time is approximately ()00 ergs/mm-. 



MoiUiti) and Beha.'ior of Protozoa. There have been a number of obser- 

 vations on the behavior and motility of protozoa during or immediately 

 following irradiation, (liese and Leighton (1935a; Giese, 1938b, 1945a) 

 have presented a series of quantitative observations on the effect of ultra- 

 violet on a variety of ciliates. In particular, Giese (1938b) gives com- 

 parative data for 50 per cent rotation on the long axis and 50 per cent 

 immobilization for Tetrahymena glaucomiformis, Colpidium colpoda, 

 Stylonychia curvata, Paramecium bursaria, P. aurdia, P. caudatiim, and 

 P. multimicronucleatum , Blepharisma undulans, Spirostomum ambiguum, 

 Bursaria truncateUa, and Fabrea salina. Giese (1945a), using monochro- 

 matic ultraviolet, has shown that the action spectrum for immobilization 

 and for ciliary reversal in Paramecium has a peak at 2804 A, suggesting 

 that it is similar to the absorption spectra for certain proteins (Fig. 8-7). 

 A variety of other studies on motility and behavior are summarized in 

 Table 8-2. 



Immobilization has been observed often and in many cases is probably a 

 sign of impending death. However, this is not necessarily so. The 

 reviewer (unpublished) has observed complete immobilization of P. 

 aurelia by 2250 A ultraviolet at a dose (1000 ergs/mm'- incident on the 

 quartz container) which not only is not lethal but has only a very small 

 effect on the time to the first division after irradiation. 



Wichterman (1948a, b) has reported in some detail the effect of X rays 

 on the mating reaction in P. bursaria and P. calkinsi. Doses in the range 

 between 100,000 and 700,000 r lessen or prexeiit the mating reaction and 

 the pair formation which usually follows from it. Apparently, pair for- 



