Discussion 33 



called spirocercosis. This disease is localized in the arteries. I have read 

 in the literature that it is very common in the Soviet Union and common 

 in parts of Europe, while it is less so in Western Europe ; I have seen 

 no publication from the United States on this condition. If, therefore, we 

 study the diseases of animals, we can explain the cause of death and we can 

 then distinguish some processes which are not due to ageing but to disease. 



Landowne: On the subject of variability, if there are multiple causes 

 which all lead to changes in one general direction with age, absolute 

 variability can be unchanged or even reduced; where data show an 

 agewise diminution, the variability may appear to increase if expressed 

 as coefficient of variability or if measures of technical variability are 

 involved. In looking for this increase in variability with age in human 

 populations we have seen all three things : increase, no change and de- 

 crease. Consequently, I wonder whether this expression of variability 

 does not depend upon the point of view you take — in the case of the 

 gonadotrophin study as an index of endocrinological change — whether 

 in each instance it may not have its own explanation rather than being 

 a fundamental biological process. 



Lorge: The issue is more complicated than that. If the gross function 

 which is death, is multiple cause, then the query is : what is the relation- 

 ship between means and their variabilities and the correlations among 

 the traits that are involved ? Any sort of variability can be produced 

 by hypothesizing what are the correlations and the means. If the means 

 are negatively associated, they give one kind of a picture. If you discuss 

 variability in ageing, the question then becomes one of isolation of the 

 relative differential components, whether factorially or in any other way; 

 and I think, at the present moment, even in biological functions such as 

 blood pressure, as you have pointed out, we don't even know what all 

 the components are. I was greatly impressed by the fact that the blood 

 pressure data here reach to ages 67 or 68. In the United States much 

 effort and money have been expended in trying to get data to the 

 hundreds. It really is most difficult data to collect. We do not know 

 what happens after age 67; and, with the increase in longevity, let us 

 say of Western European and North American populations, the problem 

 of getting people to subject themselves to blood-pressure tests becomes a 

 problem of data collection too. All in all, the problem of making an 

 assertion about variability depends on a methodological issue of the 

 isolation of the components underlying a particular overall trait, be it 

 death or blood pressure. 



Gillman: There are certain issues arising from Prof. Bourliere's paper 

 on which I think some contribution can come from South Africa. He 

 made the statement that he believed the death of many species, such as 

 lizards and reptiles, was usually accidental. I cannot agree with this. 

 Some years ago, by chance, a student of mine at the University of Wit- 

 watersrand, in investigating the haematology of reptiles, found, among 

 other very interesting things, an incidence of parasitic infections so high 

 that up to 80 per cent of one particular species of lizard in the wilds 

 were afflicted by haematological gregarine parasites. Similar observations 

 were also made in certain snakes, again caught in the wild. All these 



AGEING — III — 2 



