Enzymes in Irradiated Tissues 49 



earlier paper where the actual Qq^ and Q^^ (anaerobic glyco- 

 lysis) are given and show the great difference in result accord- 

 ing to temperature. Therefore, I consider that we have here 



a case where radiation a relatively large but not enormous 



dose — inhibits an enzyme sequence in vitro. If the retina is 

 like the tumour used in Crabtree's earlier work it appears that 

 irradiation must be carried out at 0° for the effect to occur. 



No work, as far as I know, has been published on the effect 

 of radiation on retinal metabolism in vivo. But that is not to 

 say that radiation has no effect. First of all, it is known that 

 low doses of X-rays produce a sensation of light — the X-ray 

 phosphene has been known since the last century — and there 

 is considerable evidence that X-rays act on visual purple, the 

 light-sensitive substance of retinal rod cells (Lipetz, 1955a 

 and b). This action of X-rays in stimulating the retina is not 

 known to have any relation to the inhibitory action of X-rays 

 on retinal glycolysis as the visual purple in rat retinas used 

 for metabolic experiments may have been largely bleached 

 although the retinas were prepared carefully in dim light. 

 Let us just use this as an indication that X-rays can stimulate 

 retinal tissue in vivo. 



Evidence that X-rays have a very rapid damaging effect 

 on the retina in vivo has come from recent work by Cibis, 

 Noell and Eichel (1955) who have found that a dose of 2,000 r 

 given to the eye of a rabbit abolishes the 6-wave of the 

 electroretinogram within 10 minutes of the cessation of radia- 

 tion. This change may be reversible but with larger doses the 

 rod cells of the retina show degenerative changes within 3-5 

 hours, and over a period of days these cells disappear. The 

 changes produced by X-rays are strikingly similar to those 

 produced by injection of iodoacetic acid, that well known 

 inhibitor of the enzymes of glycolysis. Noell (1951) found 

 that non-lethal doses of iodoacetate caused immediate 

 reduction in amplitude of the electroretinogram measured in 

 the living animal and gradual histological decay of the rod 

 cells. Cone cells were relatively immune, as they are also to 

 X-rays. 



