DISCUSSION 



similar. The chemical agents under discussion are rather more general in their 

 effects and are concerned apparently with the more immediate physico-chemical 

 ramifications of energy transfer, probably because they serve as hydrogen donors. 

 Tissue shielding and transplants may be thought of as procedures which do not 

 modify the initial injury but rather encourage the recovery of specific physiological 

 systems. 



Betz : Bacq has shown us his results on the depletion of the cortical cortex of 

 irradiated rats and of those irradiated and protected by cysteamine. We made 

 similar obser\ations 5 years ago, when studying the behaviour of the adrenal 

 cortex of mice protected by injection of KCN. We saw indeed that the animals 

 protected by KNC had a much less marked depletion of the cortical lipids than the 

 controls. Our observations were made on sections on the adrenal stained with 

 Soudan III. I would like to add to Bacq's comment that it is perfectly possible to 

 detect by histological means the depletion of the adrenal cortex. Even the first 

 phase of depletion occurring after 2 or 3 hours and lasting a short time is to be seen 

 histologically. 



Bacq told us about a hypothesis on the mechanism of action of some chemical 

 protectors. It is quite possible that some chemicals act by protecting a factor stimu- 

 lating the haematopoietic regeneration, or by protecting some cells producing this 

 factor. This is an interesting working hypothesis. So far as the mechanism of 

 action of the spleen and bone marrow homogenates are concerned, I would like to 

 suggest that they also act by the pathway of the nucleoprotein anabolism. Some 

 results published by Kelly and Jones show that such preparations enhance the 

 synthesis of DXA in irradiated animals. 



I know very well Patt's work on the adrenal depletion in irradiated rats and I 

 agree entirely with him. I repeated his chemical studies and found the same 

 results. The terminal drop of the ascorbic acid and cholesterol in the adrenals of 

 animals submitted to a lethal dose of X-rays seems to be a sign of hyperactivity 

 rather than a sign of exhaustion of the gland. 



I quite agree with Mole that the adrenals are necessary to the survival of irradiated 

 animals. As I showed in my papers, our adrenalectomized rats were very sensitive 

 to a whole body irradiation. Some amount of cortical hormones is necessary to 

 maintain a normal resistance. But this does not rule out the possibility that a large 

 excess of such hormone may be noxious to the haematopoietic tissues. We feel that 

 the irradiated body produces an excess of cortical hormones ; as the results shown 

 here indicate, this excess plays a role in the inhibition of the haematopoiesis we 

 observe after a lethal dose of X-rays. 



J. S. Mitchell : Although the methods of classical histology show no obvious 

 changes shortly after irradiation, studies w^hich I have carried out over a number of 

 years with the use of ultraviolet photomicrography have shown changes in cellular 

 nucleic acid metabolism in several types of cells within relatively short times after 

 irradiation. In my early worki^^is on the accumulation of pentose nucleotides in 

 cytoplasm after irradiation and inhibition of synthesis of deoxyribonucleic acid by 

 irradiation, a substantial increase in cytoplasmic absorption at 2,537 A was 

 found in a number of human malignant tumours at 80 minutes after irradiation. 

 The magnitude of the change was consistent with the presence in the irradiated 

 cytoplasm of ribonucleotides in local concentration often of the order of 3 per cent. 

 In further work^*-^* experiments using ribonuclease in conjunction with quantitative 

 ultraviolet photomicrography showed that the cytoplasmic nucleotides accumulating 

 after irradiation were mainly ribo-polynucleotides closely resembling, and probably 

 identical with, ribonucleic acid. Extraction methods showed characteristic nucleo- 

 tide absorption with maximum at the wavelength 2,620 A. It is important to note 

 that the increase in ribonucleotide absorption occurs almost entirely after irradiation 

 with doses less than the region of 750-1,000 r ; at higher doses usually there is no 



313 



