Biological Approach in Study of Ageing 17 



generalizing the phenomena we find. It would be possible to 

 obtain, within a reasonable time, a knowledge of the compara- 

 tive rates of ageing in vertebrates as full as our knowledge, 

 for instance, of their sexual cycles. This would require the 

 collection and statistical analysis of as many suitable records 

 as possible ; it could be supplemented by cross-sectional surveys 

 on domestic animals such as dogs, and possibly even on 

 specially kept populations of the larger fish and birds. I 

 think it is evident that if we could obtain vital statistics only 

 for the main breeds of dog, the information would throw 

 light on the effects, if any, of size on longevity, and of the 

 endocrine and other differences found in pure breeds and in 

 experimental crosses between them. Work on methods of 

 ageing adult vertebrates, such as that described by Bryuzgin 

 (1955) and used by Prof. Bourliere's colleagues on the ossifica- 

 tion zones of snakes (Petter-Rousseaux, 1953) is clearly of 

 great importance. I think that at present the most important 

 requisite, however, is the co-operation of those biologists and 

 others who have the data, or the opportunity to extract them, 

 but who do not know the nature of the information wanted. I 

 think a symposium similar to this one, attended by veterinary, 

 stockbreeding and conservation workers, and directed to 

 surveying available records would be of great value to the 

 business of obtaining comparative vital statistics. 



May I perhaps summarize the points I have made : our work 

 is concerned with a series of phenomena arbitrarily chosen for 

 study. They are probably similar in biological significance but 

 they may be different in detail. The measurements and 

 definitions which we use in comparative study must take this 

 into account. For this reason it is convenient to base our 

 comparisons, initially at least, on the decline of vigour with 

 age as it is measured by the increase in the force of mortality : 

 it is a prerequisite of any understanding of the evolution of 

 this decline in man that we should obtain a better impression 

 of its distribution in vertebrates, and we should devise ways of 

 doing this as soon as possible. 



