542 DK. p. CHALMERS MITCHELL ON LONGEVITY AND 



died in the first few months after arrival (by birth or otlierwise) 

 or survived to an age approaching tlie maximum, whilst in other 

 cases there was a mortality rate steadily increasing with the 

 length of residence in captivity. Obviously, the different curves 

 that would be displayed by different animals, if the individual 

 cases were plotted out in such a fashion, would give valuable 

 information as to the special periods of danger in the case of 

 different animals, and inform us if there were cases where the 

 mortality was the result of progressive and cumulative effects of 

 captivity. As, however, the facts at my disposal did not include 

 any informa,tion as to the age or condition of the animals on 

 reception, I came to the conclusion that it would be a waste of 

 time to plot out curves. 



(4) Unfortunately, collections of animals have to be considered 

 from the financial point of view. The money value of an animal 

 to a collection, that is to say, the price which can be judiciously 

 paid for it, depends on its rarity, its attractiveness to the popular 

 and scientific clients of the institution, and on the length of time 

 it may be expected to live. A gorilla, for instance, is rarer and 

 much more attractive than a chimpanzee, but as a gorilla has 

 a very much worse expectation of life in captivity than a chim- 

 panzee, its money value may be smaller. The facts that I have 

 brought together form, so far as I know, the first beginning of 

 a practical guide to the value of animals considered from this point 

 of view. 



(5) I have been able to bring together a large series of facts 

 with regard to the relation between size and longevity. Taken in 

 the broadest way, it is true that large animals may be expected 

 to live longer than small animals, and in the case of very closely 

 allied creatures the relation is frequently close. This may be 

 associated partly with the effects of the accumula,tion of waste 

 products. The cubical capacity of an animal increases much more 

 rapidly than its linear dimensions, and of two animals of similar 

 structure and constitution, the larger may take longer to be 

 poisoned by its own waste products. Of course many simpler 

 factors are involved — such as the greater resistance of a more 

 bvilky animal to rapid changes in the temperature of the air or 

 water in which it lives. On the other hand, difference in 

 longevity is not in exact proportion to size, and otlfer con- 

 stitutional factors are more important. Birds, for instance, in 

 proportion to size, have higher potential longevities than mammals; 

 whilst within the classes, orders, and even families, there are many 

 ca,ses where difference in size is overborne by other constitutional 

 differences. It seems to be the case that, in proportion to their 

 size, the more highly developed members of a group are able to 

 live longer than their lower kin. There are also a very large 

 number of cases, where increased viability and longevity are 

 a,ssociated, as Mefcchnikoff suggested, with a relatively low capacity 

 of the hind-gut. 



(6) It has long been known to aviculturists that common 



