A Fantasy on Ageing 189 



It has been reported that undernutrition in some of the flat 

 worms leads both to a reduction in size and weight and also 

 to the reappearance of immature features — in other words to 

 rejuvenation. There is no evidence that undernutrition can 

 do anything like this to the higher animals but it certainly can 

 so delay the metabolic processes that by it the normal life 

 span of an animal can be greatly prolonged. A start has been 

 made (Brody, 1945; McCay, 1952; Hammond, 1952) but 

 there is still a great deal of interesting work to be done on 

 this subject. There is as yet no indication that any of the 

 higher animals can be made immortal in the sense that many 

 protozoa may be so regarded. Specialization and integration 

 have been the cause of this "mortality" but once a cell, even 

 of a highly specialized organism, has been removed from its 

 surroundings and isolated in tissue culture the system may 

 become "immortal" and heart muscle may be kept alive and 

 beating indefinitely provided the cells are able to grow and 

 reproduce themselves. 



If undernutrition can so delay the metabolic processes that 

 it can prolong the whole life-span of an animal, overnutrition 

 can certainly do the reverse. It may not be easy to over- 

 nourish a normal animal during growth if the ideal food for 

 growth is provided for it, and our big pig is a good example of 

 this, but the fate of the mouse which has been overnourished 

 (Silberberg and Silberberg, 1954) or of the rat whose hypo- 

 thalamus has been punctured (Kennedy, 1950, 1951, 1952) 

 is a proof of what may happen provided something can be 

 done to break down the mechanism which normally adjusts 

 food intake to food requirements, and the obese child who 

 has over-eaten for psychological reasons may be considered 

 as the human counterpart of these animals. Once an organism 

 is fully grown it is generally easier to get it to eat more than it 

 requires for the energy it expends, and the insurance figures 

 leave us in no doubt about the effects of over-eating on the 

 expectation of human life. 



It is clear now that "efficiency" at all ages depends upon 

 being in the right plane of nutrition. In nature the time for 



