Enzymes in Irradiated Tissues 47 



be meaningless. Excretion of steroids after radiation seems to 

 have been little studied. It is therefore impossible at present 

 to link the in vitro depression of steroid synthesis with in vivo 

 changes. 



Effect of radiation on the retina 



Crabtree (1936) found that if he gave long periods of 

 irradiation with radium — he does not specify the dose — 

 either to tumour tissue or to retinal tissue in vitro at 0°, the 

 anaerobic glycolysis was very much depressed whereas the 

 respiration of the tissue was unaffected. Tumour irradiated 

 at 37° showed no failure of anaerobic glycolysis. Retina could 

 not be irradiated at the higher temperature as the control 

 non-irradiated retina was unstable here. 



Crabtree and Gray (1939) repeated this work using known 

 doses of X-rays, beta-rays or gamma-rays, keeping the time 

 of irradiation short and measuring the metabolism as quickly 

 as possible after radiation ended. They studied the retina of 

 the rat. Table IV shows that after a dose of 1,250 r given in 



Table IV 



Inhibition of Anaerobic Glycolysis of Rat Retina by 



x-irradiation at 0-5° 



Anaerobic glycolysis was measured 20 minutes after end of radiation 



5 minutes at 0° the anaerobic glycolysis, when measured 20 

 minutes later, had fallen by 13 per cent. As the dose of radia- 

 tion given was increased the inhibition of glycolysis became 

 more marked. Fig. 1 shows that equal doses of p-radiation 

 and of X-radiation have the same effect. A criticism of this 

 work is that the figures given are percentage decreases and 

 if one calculates back from these percentages to the actual 



