EXPERIMENTS ON LONGEVITY 



By RAYMOND PEARL 



Institute for Biological Research, The Johns Hopkins University 



(The substance of this paper was presented as a lecture, on the Schijf Foundation at Cornell 



University, May p, 1928) 



THE PROBLEM 



THERE is something fascinating 

 in the idea of experimenting 

 with longevity. The span of 

 life is a rude and uncompromis- 

 ing inhibitor and limiter in human affairs. 

 Just about the time that a man's experience 

 in living has attained a sufficient mag- 

 nitude to give him some confidence that 

 he has acquired a little skill in that diffi- 

 cult art, Death comes stalking along and 

 ends it all. Furthermore death, coldly 

 and unfiguratively considered merely as 

 a biological process, has the unfortunate 

 characteristic of irreversibility. So any 

 experimental approach to its study, with 

 man in the traditional guinea-pig role, is 

 not feasible. 



In the face of such a situation there are 

 two things which the person curious about 

 death, longevity, and similar subjects may 

 do. He may either content himself with 

 the monotonous pabulum of human vital 

 statistics — not entirely innutritious, to be 

 sure, but still a diet so narrowly con- 

 structed, so lacking in savor, and so full 

 of indigestible residues that it has a 

 tendency to induce in those who nourish 

 themselves exclusively upon it a certain 

 bilious and acidulous temperament, a 

 leptosomal habitus of body, and mental 

 delusions of righteous exactitude as irritat- 

 ing as they are unwarranted. 



Or, on the other hand, the inquisitive 

 person whose dilemma we are endeavoring 

 to resolve, may study mortality and 

 longevity experimentally, in some organ- 

 ism other than man. This means that he 

 can subject his animals to all sorts of 

 influences, completely under his control, 

 and see how their duration of life is 

 affected. Out of all this are likely to 

 come many thrillingly unexpected things. 

 On account of the general happiness and 

 good cheer thus engendered there is in- 

 duced a tendency towards a pyknic or 

 eurysomal habitus of body, and a tolerant 

 realization of the liability of human beings 

 to draw erroneous conclusions from what 

 seem — but unfortunately too often only 

 seem — to be plain facts of nature. There 

 is sound tradition for such an effect. 

 The Greeks, the Chinese, and the Hindus 

 all represented their gods as of a pyknic 

 habit, and, as everyone knows, the chief 

 activity of gods is to make biological 

 experiments with human beings. 



Not wishing to miss any of the pleasures 

 of life, I have myself tried both the 

 statistical and the experimental methods 

 of studying mortality and longevity. 

 But tonight I shall speak to you only 

 about the results reached by the latter 

 method. In short our discourse is to be 

 about such lowly organisms as flies and 

 muskmelons, and has nothing whatever 

 to do with man directly. Perhaps the 



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