482 ItADIATlOX MIOLOGY 



Similar results have been obtained on the same material by Marshak 

 (1949a, b), who. iio\ve\<'r. could not deteet photoreaetivatioii in unferti- 

 lized e^ifzis. This author explored the possibility of some chemical actions 

 in the ultraviolet effect and in photoreactivation by treating samiMcs and 

 zygotes, before, during, and after irradiation with ultraviolet and visible 

 light, with the following substances: adenine, streptomycin, foli<- acid. 

 4-amino-//-methyl folic acid (a folic acid antagonist), and riboflavin (on 

 reactivation of zygote only). None had any effect. 



Wells and Giese (1950) have investigated llic photoreactivation of the 

 cleavage delay subsetiuent to ultraviolet treatment in gametes and zygotes 

 of the sea urchin Strong ylocentrotus purpurahis, with experiments similar 

 to those performed by Blum and coworkers. Wells and Giese used for 

 inactivation monochromatic ultraviolet obtained with a quartz mono- 

 chromator, and compared the photoreacti\ability of delay produced by 

 several wave lengths between 2450 and 3130 A. It appears that photo- 

 reactivation occurs in eggs treated with ultraviolet of all wave lengths 

 tested with similar efficiency except at the shortest wave lengths, 2450 A. 

 where photoreactivation is reduced. This wave length has a strong effect 

 on the surface of the eggs, w^hose membrane is raised. The lower photo- 

 reactivability of eggs damaged by treatment with this wave length is 

 attributed to ultraviolet damage to the surface membrane. 



Wells and Giese found that sperms are considerably damaged by the 

 photoreactivating light, so that photoreactivation cannot be detected 

 readily. A small amount of photoreactivation could, however, be demon- 

 strated also on the naked sperm, contrary to the findings of Blum. 

 Robinson, and Loos (1950) with Arbacia. 



The most effective spectral region for photoreactivation in Strongi/lo- 

 cenfrofus gametes and zygotes lies betAveen 3660 and 4300 A. 



10. PHOTOREACTIVATION IN SALAMANDER LARVAE 



Blum and Matthews (1952) studied the effect of photoreactivation on 

 the killing effect of ultraviolet radiation on larvae of Amblystoma macu- 

 latum and -4. opacum. When the larvae were irradiated with a single 

 massive dose of ultraviolet, no photoreactivation took place; but when the 

 larvae were exposed to repeated low ultraviolet doses, each being followed 

 by exposures to the photoreactivating light, the fraction of surviving 

 larvae was much greater in the light-treated group than in that kept in 

 darkness. It is remarkable that the effect of photoreacti\'ation was still 

 present when the larvae were treated with light 20 hr following ultraA'iolet 

 exposure; in all other organisms photoreactivability is generally lost 

 within a few hours. The spectral region in which the photoreactivating 

 light was active is similar to that observed in other organisms (3000- 

 5000 A). 



