Discussion 249 



experiments at almost the same time. He did not exclude subjects with 

 elevated blood pressures and his results on British subjects are almost 

 identical with those we found by excluding the individuals with ele- 

 vated blood pressures. 



Scribner: The question posed by these data is: is the change in the 

 kidney function, as described, a result of disease in the kidney or a 

 wearing out with age, or is it simply a response to a decrease in the size 

 of the living organism? This all comes back to the point raised by Prof. 

 Heller and Prof. Borst: might not creatinine excretion, or total ex- 

 changeable potassium, be reasonable reference points? 



Shock: We have done a good many creatinine determinations in 

 balance studies under conditions of a closely regulated diet. However, 

 I have never been able to convince myself that creatinine excretion gives 

 a stable value that is characteristic of the individual, because we have 

 seen some rather wide fluctuations that we have not been able to explain 

 satisfactorily. I tried it first with adolescent children and then gave it 

 up as I did not feel it could be determined as a characteristic constant 

 for the individual. But I am intrigued by the potentiality of the total 

 exchangeable potassium, and would like to study its changes with age. 



Bull : The lines you showed in illustrating the decline of renal function 

 with age are practically identical with the lines for our mortality findings 

 in burns. By Probit analysis we can fit LDjo's for the areas of burning 

 which will produce death at different ages. It may be coincidence that 

 you chose your ordinates on just the right scale, but the lines are almost 

 the same in that they take off at just the same age and go down in the 

 same way. Burning is a severe stress. We have been talking about the 

 elderly having a reduced tolerance to stress, and burning is largely a 

 stress affecting water and electrolytes. The burn is a convenient 

 measurable lesion, and death occurs with a progressively smaller size 

 of burn with advancing years, which I think probably represents an 

 important aspect of the ageing of a regulation of water and salt. 



