50 Antoinette Pirie 



Various considerations come to mind. First, is the rapid 

 diminution of the electroretinogram due to bleaching of the 

 visual purple by the X-rays? This seems unlikely since 

 Lipetz (1955&) using isolated retinas found little bleaching 

 until 10^-10^ r were given and then the picture was muddled 

 by heating effects. Calculations based on ratio of threshold 

 dose to bleaching dose for light and for X-rays also predict 

 that a very large dose of X-rays is necessary for bleaching. 

 Second, is the change in electroretinogram and the degenera- 

 tion of the rod cells due to vascular change in the choroid? 

 Cibis, Noell and Eichel (1955) state that vascular engorgement 

 occurs, but it is said that this type of retinal degeneration 

 would not be expected from such choroidal change. 



With a dose of 1,400 r of X-rays we have noticed degenera- 

 tive changes in the outer limbs of rod cells of the rabbit eye 

 when the animal was killed some weeks or months later. 

 We have not examined many animals. Biegel (1955) using 

 radiation from the betatron failed to find more than minimal 

 changes after 3,600-4,500 r, in the rabbit retina. The results, 

 therefore, are a little variable. 



In trying to assess the effects of radiation on the retina let 

 us return to the work of Crabtree and Gray. At 0° the 

 anaerobic glycolysis was inhibited. Now at 0° Terner, Eggleston 

 and Krebs (1950) have shown that retinal tissue is unable to 

 maintain osmotic control. It loses K and takes up Na. Low 

 temperatures have, in fact, a most remarkable effect on tissues. 

 It has long been known that they swell at this temperature, 

 and Conway, Geoghegan and McCormack (1955) find that 

 kidney and muscle tissue frozen in liquid O2, ground up and 

 then maintained at 0°, lose ATP and hexosephosphate and 

 increase their non-protein N. Hence, if one irradiates a tissue 

 at 0° not only is it in a state of metabolic arrest but it will be 

 in a state of metabolic decline. The change in K and Na in the 

 retina at 0° are reversible at 37° in the presence of glucose and 

 glutamate but not in their absence. 



It seems possible that radiation could have a quite different 

 effect at low temperatures from that at normal — without 



