206 General Discussion 



regenerates its antlers ever>' year. Antlers ean be eollected and weighed 

 and analysed or even studied when they are growing. It is a beautiful 

 animal for studying the ability to regenerate. Here is a reproducible 

 growth impetus every year, it goes down gTadually as the animal grows 

 older. But you can change the development of the antlers, you can 

 control it by changing the endocrine environment. 



Lansing: There is a very large literature on the role of nutrition in 

 experimental animals. It doesn't need another fifteen years to be 

 resolved, it has been resolved for more than fifteen years — some of the 

 work was done in about 1900, on silk worm, Cladocera (Daphnia in 

 particular), on rotifers, on Planaria and other fiat worms, even on rats 

 and mice. Hoelzel and Carlson several years ago published extensively 

 on this subject, and I'm surprised at the amount of general agTcement 

 there is. The consensus is, with amazingly little difference of opinion, 

 that restriction of the diet prior to maturation does seem to effect a 

 prolongation of life-span — restriction of diet, or super-alimentation, 

 after maturation, having no effect at all. 



Shock: But isn't the problem that we are raising here a little deeper 

 than that? We are asking "what is the mechanism whereby this pro- 

 cess is carried out"? It seems to me that although we do have a fairly 

 large body of information on various animal species, we have not yet 

 any fruitful ideas on the mechanism of the process. 



McCay: In the other direction (and in regard to Dr. Olbrich's question), 

 we have left a substantial group of rats to become middle-aged and fat, 

 and then forced some of them to become tliin by exercise or restriction 

 of food, and that lengthens the life of the rat — not as significantly as 

 retarded growth, but one does get a significant result. 



Tunbridge: You have some work on your mental patients, haven't 

 you, relating to the calorie requirements in elderly people? Is it correct 

 that their calorie intake is diminished? 



McCay: There is work on that, but I didn't do it. That gets involved 

 with basal metabolism. It looks as if evidence is very good that the 

 BMR drops in older people, but I've never found any sound evidence 

 for any experimental animal that the BMR drops with age. Assuming 

 those data are sound, man may be unique in that respect. 



Shock: I think Davis (Amer. J. Physiol., 1947, 119, 28) studied the 

 basal oxygen uptake of rats, and as I recall found a reduction in the 

 basal metabolism of the rat as well as in man. 



McCay: We have data on both sides — you'll find one can jump either 

 way. 



Shock: We have collected evidence on changes in basal metabolism 

 with age, and it is true that the oxygen uptake of the total animal 

 diminishes as the individual gets older (Shock and Yiengst, 19.5.5, 

 J. Geront., in press). But if one uses some other estimate of the amount 

 of functional tissue present, instead of surface area which is our usual 

 standard, there is no change in basal oxygen uptake with increasing age. 

 We have, for example, measured the total body water content in 

 individuals in parallel with our determinations of basal oxygen uptake 

 — and when one computes the oxygen uptake per unit of body water, all 



