Physiological Approach in Study of Ageing '28 



and it is quite probable that similar differences exist in the 

 rate of ageing of most organs and functions. What is already 

 known of the disparities in growth pattern and in comparative 

 incidence of certain degenerative diseases in both groups 

 supports that idea. 



As the various kinds of animals, even among vertebrates, 

 do not age in the same way, comparative biology of senescence 

 should help in distinguishing between the basic processes and 

 modifications which are merely idiosyncrasies. When one 

 considers, for instance, the unequal distribution of athero- 

 sclerosis among the various vertebrate groups, one is com- 

 pelled to admit that the role of such a degenerative process in 

 ageing phenomena has been greatly overestimated. I myself 

 have dissected many old fishes, reptiles, passerine birds, 

 rodents and even primitive lemurs without finding much con- 

 clusive evidence of atherosclerosis. 



More important than that, the comparison of age changes in 

 various phyla of the animal kingdom should help us to isolate 

 their "common denominator". Besides the usual laboratory 

 animals — and the senile hospital patient — the experimental 

 gerontologist should certainly take advantage of a closer 

 study of some "natural experiments" which could seldom, if 

 ever, be performed under laboratory conditions. 



To illustrate that point, I should like to recall a few ob- 

 servations and experiments which seem to indicate some 

 correlation between the rates of energy-turnover and ageing. 



Fifty years ago, Rubner (1908) was the first to propose a 

 definite relationship between rate of metabolism and duration 

 of life. He believed that various mammals during their life- 

 times used up approximately the same number of calories per 

 unit of weight. As the smaller species have a much higher 

 rate of metabolism per unit of weight than the larger forms, 

 in order to preserve a constancy of body temperature, their 

 duration of life should accordingly be shorter than those of 

 bigger species, and such is actually the case. Rubner did not 

 furnish any experimental evidence to support his idea, and his 

 theoretical work was even challenged by some authorities. 



