Discussion 265 



DISCUSSION 



Gerking: Did McCay keep these trout you mentioned until they 

 died? You referred to an increased Hfespan for these fish. 



Rockstein: My recollection is that he was able to double the life- 

 span of the trout. 



Comfort : The total duration of the experiment was only a matter of 

 months, while they were in the hatchery. The lifespan of trout is at 

 least 10 years. 



Berg: The advantage of using rats for lifespan studies is that we 

 can determine causes of death in this species, whereas the pathology 

 of other species has not been studied as thoroughly. 



Rockstein : We are not as fortunate as you in having a pathologist. 

 There are insect pathologists, but they are very rare and very 

 costly. 



Berg: McCay employed drastic underfeeding so that his animals 

 were severely retarded in growth and did not attain sexual maturity. 

 The greater longevity of McCay's rats has been attributed in part 

 to the retardation of sexual development. In our experiments, 

 sexual maturity of the females was delayed only three to four weeks, 

 and skeletal measurements were only 5 to 7 per cent less than in ad 

 libitum-fed rats. These findings indicate that longevity of the rat 

 can be increased by dietary restriction without seriously affecting 

 skeletal growth or sexual maturity. 



Rockstein: We are all eagerly awaiting the results of your experi- 

 ments on longevity. 



Comfort: 1 am a little disturbed, Prof. Rockstein, about drawing 

 analogies between the nutritional requirements of rats and those of 

 insect imagos. For example, I take it there is very little extragonadal 

 mitosis in your flies. Any change you get is not due to altering the 

 number of cell generations or the stage of development. 



Rockstein: No, I did not mean to draw that analogy. I should 

 have mentioned that adult flies are essentially fully-grown animals, 

 much like the honey-bee, but even more so because the honey-bee 

 takes about ten days to attain full maturity. The housefly on the 

 other hand is completely mature within a few hours except for the 

 ability to lay fertile eggs, under standard laboratory conditions. But 

 I did mean very definitely to compare the human with the rat, and 

 to emphasize that starvation would hardly be of any use in the 

 human if one wanted to prolong life. I do not know that it has ever 

 been shown to do so; if anything, it would shorten the lifespan in 

 man. When McCay and his workers came out with the pronounce- 

 ment that a low protein, low calorie diet was what we needed for a 



