Physiology 487 



Strom units) to 1.5 m^i or less. Rays of 390-200 m\i are transmitted through 

 quartz and are sometimes termed the "quartz spectriun." Below 200 m[x 

 lies the Schumann-Lyman-Millikan region in which the rays are absorbed 

 by water, air, and most other materials. In the Schumann range (approxi- 

 mately 200-125m[j.), fluorite is used for transmission. 



The reported effects of ultraviolet irradiation vary with the wave 

 length, the dosage, the species, and physiological condition of the organ- 

 isms (155). In the quartz spectrum, radiation is relatively harmless at 

 the longer wave lengths. Heavy dosage at 313 m[K is not lethal to Para- 

 mecium multimicromicleatum (157), and there is almost no effect on 

 Euglena at 313 and 365 va^. (543). Excystment of Colpoda duodenaria is 

 slightly retarded at 313 mjj, in a dosage of not less than 30,000 ergs/mm^, 

 but tripled dosage at 366 mjji, is without effect (153). Peraneyna tricho- 

 phorum is killed at 253 m[j, but not at longer wave lengths (523). Radia- 

 tion at 302 m[j, in a dosage of 28,000 ergs/mm^, and also the shorter wave 

 lengths in lighter dosage, are lethal to P. midtijnicronucleatum (157). 

 Selective effects of particular wave lengths have been noted. Motor re- 

 sponses of P. trichophorum are most rapid at 302 m[x (523). Fission of 

 Paramecium caudatiim is retarded more markedly at 280.4 than by equiv- 

 alent dosage at 265.4 m^., although recovery from exposure to the longer 

 wave lengths is more rapid. This difference in rate of recovery is attrib- 

 uted to greater absorption by nucleoproteins at 265.4. Since absorption 

 is essentially the reverse for cytoplasmic proteins, fission is delayed to a 

 greater extent at the longer wave length (152). At a particular wave 

 length, the specific effects may vary with the dosage. At 280.4 nirj,, im- 

 mobilization of P. caiidatiim requires about 11,800 ergs/mm^, while fis- 

 sion is retarded by 2,000-3,000 (154). 



Effects of ultraviolet vary also with the species. Fabrea salina is about 

 six times as resistant as Tetrahymena pyriformis and the latter is twice as 

 resistant as Blepharisma undulans and Spirostomiim amhiguum to radia- 

 tion at 253.7 n\]). (151). Differences also have been noted within the genus 

 Paramecium and among several strains of P. multimicronucleatum (158). 

 Physiological condition of the organisms also influences susceptibility. 

 Tetrahymena pyriformis in old cultures is much less resistant than in 

 young populations (151), and starved specimens of Paramecium are more 

 susceptible than well-fed ciliates (158). Sensitivity of P. caudatum seems 

 to be greatest in early stages of fission (201). Sensitivity of Paramecium 

 also increases with rising temperature within the range, 0-30° (96), and 

 preliminary exposure to ultraviolet increases susceptibility to high tem- 

 peratures (23). 



Effects on fission also have been noted. Fission of P. caudatum may be 

 accelerated by light dosages (3, 201), and in the absence of serious injury, 

 recovery from heavier dosage may be accompanied by accelerated fission 

 (24). Still heavier dosages retard or inhibit fission (3, 152, 201, 524), and 



