GENEEAL DISCUSSION 365 



which they examined the physico-chemical properties of hundreds of 

 protective substances, the thesis is proposed that not every anti- 

 oxidant is a ])rotective substance. However, not one such protective 

 substance is known as yet which does not possess anti-oxidant pro- 

 perties. We must recognize that all the existing defence substances 

 are inhibitors of chain oxidation reactions, and the restricted nature of 

 their action is explained by the presence of non-oxidizing primary 

 reactions. In order to have total protection, it is necessary to seek 

 certain other substances which are not oxidation inhibitors. 



ZELENY : In the systems of connective tissue investigated by Brinkman 

 the oxygen pressure was measured and its protective action shown. 

 It seems obvious that this is explained by the interception of the H 

 radicals, because cysteamine also has a protective action in these 

 systems ; I would like Bacq to give us his views on the nature of the 

 action of cysteamine in this tissue. 



BACQ : The action of the cysteamine in these systems does not depend 

 upon the oxygen tension. Bisulphide derivatives and tryptamine which 

 do not contain - SH groups and even sulphur have an analogous effect. 

 It is possible that polysaccharides or hyaluronic acid in the connective 

 tissue is transformed under the action of radiation to an excited state, 

 and in the presence of a hydrogen donor is returned to the original 

 condition. 



SEMENOv: The damage to the bone-marrowy the intestines, the skin 

 and other proliferating organs of mammals given doses of 200 to 700 r 

 may not involve the mechanism of cellular death. In this case, the ces- 

 sation of biosynthesis and the gradual depletion of the materials accu- 

 mulated for the reproduction of the cells is of fundamental significance. 



In this case, when carrying out investigations, it was necessary to 

 examine how the protective substances affect the basal cells and not 

 the differentiated cells such as leucocytes, lymphocytes, reticular cells 

 in the bone-marrow, etc. 



Thus what is of interest is not the action of the protective substances 

 on the so-called radiosensitive cells but the action on the insensitive 

 cells, which are the source of the production of the sensitive cellular 

 elements. When examining the mechanism of the local protective 

 effect, this possibility must be taken into account. 



EOMANTSEv: The concept that has the greatest experimental founda- 

 tion at the present time, from our point of view% is that concerning 

 the mechanism of action of chemical protective agents according to 



