Discussion 31 



the end of the first year and very nearly the whole population die by the 

 end of the third year. What the explanation of that is, I don't know. I 

 think we must try to find a way of measuring the dose of life which will 

 prove fatal to any given individual, before it has actually proved fatal 

 to him. 



Olbrich: Do you know from which diseases your animals suffer or 

 suffered, Prof. Bourliere, and for how long? Do you know the frequency 

 of illness in your animals ? In human beings we do know. Do you include 

 all diseases or illnesses interfering with lifespan and, perhaps, also with 

 processes of ageing? The process of ageing is a doubtful business alto- 

 gether. Until now neither biologists nor scientists could present any 

 evidence saying : "These are the signs and symptoms of ageing only and 

 not of a disease." For example, the low basal metabolic rate is a very 

 important and interesting subject, and every year different results are 

 published on it. Nagorny, in 1939, published the results of his investi- 

 gations on people aged between 90 and 100 and found that they had 

 normal basal metabolic rates, normal blood sedimentation rates and so 

 on — in fact, all findings were normal. Now, if it is true that humans with 

 low basal metabolic rates live longer, then in myxoedema they should 

 survive longest, but unfortunately the clinical experience does not bear 

 this out. Another important point is that you can prolong the life of 

 patients by starving them. We do this in our clinic ; I do it to myself as 

 well. Now you advise me to put them into ice-cold temperatures — and 

 that is very difficult for me — and to let them sleep for twelve hours! 



I do not understand, firstly, what factors of disease influence these vital 

 statistics or these curves in the excellent studies of both Dr. Comfort and 

 Prof. Bourliere, and, secondly, whether one single factor — either basal 

 metabolic rate or food restriction — has anything to do with prolonging 

 life or influencing resistance to disease. 



Bourliere: The data on the comparative incidence of various infections 

 and degenerative diseases in the different zoological groups are so scarce 

 that it would be dangerous to generalize. Some studies have been made 

 which tend to show that, in mammals, arteriosclerosis is more common 

 in ungulates and in some carnivores, whereas it is quite rare and even 

 absent in most rodents, insectivores and bats. In birds the same disease 

 seems to be more common in birds of prey than in passerines. The cause 

 of these differences remains unknown, but the role of the dietary differ- 

 ences is probable. With regard to cancer, we are better documented, 

 but the gaps in our knowledge are still very numerous. It has long been 

 said that cancer does not occur in fishes and reptiles, but that is wrong. 

 Numerous observations have shown that certain types of cancer may be 

 observed in those animals. But one must not forget that in natural 

 populations very few individuals actually die from disease; most die 

 from accidents, mainly from predation and parasitism. 



Olbrich: Disease is also an accident! 



Bourliere: Yes, infectious diseases are a kind of parasitism very 

 poorly known in "lower" vertebrates. But their role as a mortality 

 factor is probably less important in natural populations than in domesti- 

 cated ones. Recent ecological studies on wild bird and rodent populations 



