30 General Discussion 



retarded again and kept in a state of suspended development, or was it 

 all or none? 



McCay: I've never let them first beeome sexually mature and then 

 stopped them. You'd ereate another variable there, the variable of 

 body-weight and adipose tissue. We have taken rats half through life 

 and then foreed them to become very thin, and again, "the thin rat goes 

 to the funeral of the fat rat". 



Comfort: That was a rather separate effect, wasn't it? 



McCay: Yes, that's a separate effect that you run into as soon as you 

 try that type of experiment beyond sexual maturity. 



Comfort: I have a medical bias here, because while it would be nice to 

 keep patients in an arrested state as children, as you kept your rats 

 children, the real medical problem is to prolong the period of adult 

 vigour. And although, I suppose, restriction of diet is beneficial, you 

 have no evidence so far that one can bring about the same slowing down 

 of the record in adult rats that one can in young ones. 



Olbrich: Dr. McCay, did you measure any type of function, say liver 

 function, in your retarded rats for a prolonged period and correlate it 

 with the time? 



McCay: No, I never did. In our hands rats are difficult for functional 

 measurements and we'd always hoped we could get dogs where M^e could 

 make functional measurements. 



Olbrich: Have you any impression that range of function is correlated 

 to time changes in a mathematical fashion in your retarded rats? 



McCay: No, I couldn't answer that. 



Olbrich: They don't get any infection? 



McCay: No. We have no trouble with infection — that's a virtue of 

 the rat, and we hope Prof. Verzar's functional tests continue to develop 

 and we'll apply them to the retarded rats. 



Krohn: Have you any notion about what is happening that prevents 

 actual maturation of the reproductive tract? Is there any particular 

 reason why the gonadotrophins should fail to be produced in your own 

 animals? 



McCay: No. We've been trying to find out how late in life the rat can 

 reproduce. Asdell made initial studies on the ccstrus cycle a long while 

 ago, but now we are actually trying to breed them very late in life after 

 they've long been retarded. We are using those same rats for certain 

 types of psychological testing at present. We're also hoping to use 

 parabiosis, and suture a retarded rat to a rat that's growing old. 



Lansing: There have been a number of studies in lower organisms 

 which show that retardation through dietary control is effective only 

 prior to maturation during the period of gTOwth, in the Cladocera and 

 so on; that if the dietary restriction is controlled after maturation there 

 is no beneficial effect, in fact in some studies there was actually a 

 reduction in total life-span. The extension of life-span is not 

 directly proportional to the period of extension of the growth 

 period, in fact there is a very great disproportion. One or two days' 

 extension of the growth period will result in a 10- or 20-fold increase in 

 life-span. 



