General Dtscusston (57 



McCance: This has been to me a delightfully simple exposition of a 

 difficult field of physiology. Now that everyone is so depressed about 

 people getting old, and the diniciilty of finding jobs for them, I'm 

 rather pleased to sec that they don't take up carbon monoxide so rapidly 

 as I do perhaps I suggest some of the old men are organized into 

 teams for rescuing })eople from gas-filled rooms. 



Verzdr: A very similar old-age illness seems to occur in rats. My old 

 rats die of emphysematous bronchitis, and so far as I know. Dr. McCay's 

 rats, which have been studied by Dr. Saxton, also died of emphysema or 

 bronchiectasis, so there might be a possibility of studying the problem 

 experimentally in rats. 



I also want to ask how far tlie decrease of lung volume which you 

 found in old cases is a functional one? Have you tried changes by 

 adrenaline or ephedrine sprays in these cases? That might show that a 

 part of it is functional and is caused by a decrease of skeletal muscle 

 tone, and not by elasticity. 



Christie: I'm very grateful for the suggestion about rats, as curiously 

 enough this has never crept into the literature on emphysema. I was 

 under the impression that horses were the animals that got emphysema, 

 and it's very difficult to establish a colony of horses. 



With regard to the second point, it is true of course that it is difficult 

 to separate the viscous resistance due to resistance to air flow from 

 tissue viscous resistance. The straightforward method of doing it is to 

 make these measurements while breathing gases of different density: 

 that is really the only approach. I would say that antispasmodics liave 

 no effect on older individuals. They do on some of the emphysema 

 patients, but not all of them. In emphysema it is a mixture usually of 

 bronchospasm and emphysema. So my reply would be that all the evi- 

 dence suggests that this is a tissue change rather than airway resistance 

 change. 



Tunbridge: You indicated that there may be a change, rather more 

 marked, at another age period than thirty-five. Is it a steady diminu- 

 tion, or is there indeed a bit of a kink? 



Christie: We have analysed it in that way, of course, but the numbers 

 are not sufficient to demonstrate a trend in any individual age group 

 after the age of thirty-five. They can only be treated as a whole. If we 

 had four or five times the number, then we might be able to treat them 

 in the way you suggest, but at the moment we can only deal A\ith them 

 as one single group. There does seem to be a general trend upwards with 

 age, but that is an impression, not a statistical fact. 



Schulze: Recently some Swiss physiologists have made microphoto- 

 graphs in rats by a thorax window, thus estimating the speed of blood 

 flow in the lung vessels. Do you know whether there is an influence of 

 ageing on the speed of the blood flow through the lungs which can be 

 measured by any method in man too? 



Christie: I don't think the microscopic method has been applied to 

 man, but there are of course several methods of measuring the rate of 

 blood flow through the lungs. I don't know of any evidence that suggests 

 that the rate decreases or increases. I myself have not approached this 



