GENEKAL DISCUSSION 345 



chemical condition of the connective tissue. If one does only anatomical work it is 

 dangerous because — even A\ith tlie electron microscoiie — everybody works with a certain 

 idea and very likely, consciously, or unconsciously, chooses the picture which suits best 

 the idea that one has. So that it would be interesting to have some biochemical test just 

 similar to the one we have at the present time for haemoglobin synthesis. One doesn't do 

 simply a histological examination of the bone-marrow with ^Te it is easy to estimate 

 the total capacity of the bone-marrow to synthesize haemoglobin. Has anybody done 

 experiments on the rate of renewal of the mucopolysaccharides immediately, or a long 

 time, after irradiation? 



BRiNKMAN: I would remark that it would not be sufficient to study mucopolysaccharides 

 biochemically because you cannot thus study the degree of depolymerization and I think 

 that this is very important. You must study it in a functional way by measuring mecha- 

 nical resistance and so forth. If you want to know something about regeneration, you can 

 learn it very simply by the injection pressure technique I described and, in this way, you 

 generally find rather a rapid regeneration in say two to three hours. To the collection of 

 hormones which you already mentioned which have an influence on this process, I 

 would like to add tri-iodothyronine which is, in my opinion, the most potent of them all. 

 We know that tri-iodothyronme has very mteresting properties in accelerating the rate of 

 mucopolysaccharide production, and this might be of some importance for extra- 

 cellular protection. 



CURTIS: We have tried tri-iodothyronine as far as the long-term effect of radiation is 

 concerned, and Dr. Nixon of the Sloan-Kettering Institute, with whom we worked, has 

 tried it in clinical experiments on recovery from radiation burns. In both cases — in our 

 experiments with animals and his with patients, there was no effect at aU with tri- 

 iodothyronine. 



UPTON: What late effects were you examining, Dr Ciu-tis? 



CURTIS: Simply longevity. We were trymg to see whether there was perhaps a difference 

 in tumour production, but we found nothing there. Dr. Nixon, of course, was simply 

 looking for recovery in the burned area of skin. 



BACQ: It may be that the normal concentration of thjTOxin and tri-iodothyronine circu- 

 lating in the blood is already optimal so that if you give more you cannot have any 

 improvement. Your control must not be a normal animal but a thjToidectomized animal. 

 We have done so, with success, in another type of experiment involving no radiation. 

 UPTON: I understand you've called for comments on the effects of radiation on connec- 

 tive tissue. I find myself wondering whether the apparent lack of effects of less then 

 optimal amounts of radiation on the age-dependent changes in coUagen may not be 

 correlated with the fact that collagen is a relatively inert material and not subject to 

 renewal throughout life. I beheve that the effects on the mucopolysaccharides of connec- 

 tive tissue cited by Dr. Brinkman have also been observed by SobeU. This, on the other 

 hand, is a moiety of connective tissue which is renewed periodically in the hfe of the 

 individual. Do you thuik that there could possibly be some correlation between the lack 

 of effect on non-renewable materials and the effect on the renewable materials of the 

 connective tissue system. 



brinkman: It has been shown by Neuberger with the aid of labelled glycine that the 

 coUagen in the cells is renewed aU the time. It is only the fibrous form wliich is not active 

 in tliis way and wliich disappears; but this is replaced by new fibres from the fibroblasts. 

 UPTON: Do I understand then Dr. Brinkman that extra-ceUular collagen fibres are in fact 

 renewed periodically, that there is a turnover? 



brinkman: Yes. In older animals it would be very slow, but in young animals it is quite 

 rapid. This holds also for elastic fibres. They are renewed rapidly from the ground 



