General Discussion 247 



which is meant a process of unfavourable, regressive, terminal 

 changes which ensue after maturity (Lansing. Problems of Ageing, 

 The Williams and Wilkins Co., Baltimore, 1952). Ageing, as thus 

 defined, is inversely related to growth and maturation and involves, 

 instead, a decrease in efficiency of the mechanism for reconstruction. 



Amoroso : Might I suggest that we define senescence as a series of 

 changes most of which, commonly but not invariably, occur in an 

 individual who has lived through a definite period of chronological 

 time? 



Williams : Is not ageing a good thing and senescence a bad thing ? 



Huggett : If I might make a suggestion : three things we want to 

 clarify, to my mind ; ageing — just call it chronological changes, and 

 not try to qualify that; senescence — an age change associated with 

 reversed growth; and growth itself may be defined as a positive 

 balance of nitrogen and other chemicals with new tissue formation 

 and increased functional usage, especially in the highest nerve 

 functions. In growth we have got greater functional usage and that 

 tends to reverse in old age. We have got new tissue formed, which 

 I think is the essential point, and there is a chemical and a physical 

 aspect to it by defining it in terms of nitrogen and possibly phos- 

 phorus. 



Amoroso: It is possible, however, to maintain speculative doubt 

 whether the changes of senescence are wholly inherent and inevitable 

 in the course of life. In the first place there is, as Professor Montagna 

 remarked this morning, considerable variability in the time of onset 

 of these changes. Secondly, in certain forms of life "ageing", as 

 we commonly understand the term, probably does not occur. This 

 is especially true of insects, many of which die showing no wear and 

 tear such as are accepted as the usual prelude to senescent changes in 

 higher animals. A notable exception is the worker bee — the in- 

 domitable woman of the hive. In the third place there is the irregu- 

 larity of the distribution of these changes within organs or tissues, 

 and finally there is the riddle of marine life, some authors main- 

 taining that in natural conditions growth of fish may be unlimited 

 by time, yet they retain their fertility. 



Montagna : Not only marine but also fresh water fish. 



Bourliere: And also all cold-blooded vertebrates. You have the 

 same thing in reptiles, for instance. But one must not forget that if 

 growth persists during the whole life-span in such lower vertebrates, 

 there is a decrease in fertility in the oldest females (Bourliere, F. 

 (1953). Joshiah Macy Jr. Foundation, Transactions of the 15th 

 Conference on Problems of Ageing, p. 126). That has been proved in 

 both fishes and snakes. Warm-blooded and cold-blooded vertebrates 

 thus do not age in the same way. 



