310 HERMAN B. CHASE 



is attributable to a fault in the design of the experiment. The results are true 

 but there was an extenuating circumstance. On the irradiated side frequent 

 pluckings were made to study the change in whiteness with time. The 

 irradiated, or white side, was plucked in some cases as many as ten times, 

 whereas the control side was i^kicked only two or three times. The irradiated 

 area was therefore maintained m a relatively rejuvenated condition by the 

 continued induced hair regenerations. In later experiments it was found 

 that the rejuvenation by continued plucking did indeed cause less keratosis, 

 less epidermal pigmentation, etc. By keeping the skin working, there was no 

 doubt that it remained "younger" by the criteria employed. 



Another point to be made is that ageing is an increase in variance, an 

 increase in the variability of a response. In studying the ageing responses 

 already mentioned, it is observed that there is a decided increase in varia- 

 bility of all of them, including epidermal pigmentation, the test for collagen, 

 etc. Most interesting is that even in some very old animals, the level for 

 epidermal pigmentation, for instance, may remain at the low level but other 

 individuals will have a considerable amount, consequently there is a great 

 increase in the variability of the response. The average response and the 

 variance increase, but some animals for a particular response will remain at 

 the "young" level. 



At a much higher level of irradiation, 2,000 r, there is more damage which 

 is also reflected as an increase in variance. At 750 to 1,000 r, even without 

 plucking to initiate new hair growth, radiation will result in more skin 

 replacement, therefore rejuvenation, than on the control side. 



DISCUSSION 



BACQ: We have been working on local injection in mice with a varietj^ of protectors, 

 mainly for epilation tests in extremely young mice between 5 and 8 days old. They epilate 

 very nicely something like 6 to 8 days after irradiation. It is an acute not a late effect but 

 what we have seen is this, if you mject cysteamine here with a needle you have signi- 

 ficant local protection and tliis is a way to investigate also the mechanism of action of 

 various protectors. Histamine gives complete protection of the animal against total- 

 body irradiation and this enables one to differentiate between local effects and general 

 pharmacological effects. Recently we have been interested, because of the many contri- 

 butions of Prof. Bruikman and Dr. Lamberts, in the possible effects of macromolecules 

 on tliis test. Synovial fluid which contams a liigh proportion of hyaluronic acid, fresh 

 human serum, or serum from the same species of mice are extremely effective in decreas- 

 ing the epilation, not only when injected before the irradiation but also when injected 

 somethmg like 20 seconds or 30 minutes after total irradiation of the animal with a dose 

 of 550 r at a rate of 150 r per minute hard X-rays. Now, normally this is an acute experi- 

 ment and I have kiUed all the animals, but after this discussion and after the paper given 

 by Prof. Chase, I am going to keep some of these animals for a long time and see what 

 happens to the skin as compared to unprotected, but similarly irradiated, skin. As far as 

 pigmentation is concerned there is also a remarkable protective effect. There is no 



