114 Discussion 



Olesen: It appears from Dr. Friis-Hansen's material that chemical 

 maturity occurs about the age of twelve months. 



Widdowson : Have you made any calculations of the body fat at differ- 

 ent ages? 



Olesen : I have tried to compare the different groups and it seems that 

 there is a relative increase in body fat throughout childhood. It is a 

 slight one but it does exist if we accept that all the non-cellular solid 

 changes are changes in body fat. This calculation is quite apart from 

 possible changes in body minerals and I do not know to what extent 

 these would interfere. 



Borst : Is there any relationship between the creatinine output and the 

 intracellular fluid? 



Olesen : In the original description of the method of determination of 

 total exchangeable potassium from Dr. Moore's laboratory (Corsa et al. 

 (1950). .7. clin. Invest., 29, 1289), a relationship was found between 

 creatinine excretion and the amount of total exchangeable potassium. 

 This has not been studied in this particular series. 



Heller : How far is it justifiable to take mean figures from ten young 

 adult females without considering the role of the menstrual cycle? Have 

 you had enough cases to pay attention to this point? 



Olesen: No, but it would appear from what Dr. Swyer mentioned 

 yesterday that it would not mean very much, as the latest view is that 

 these body weight changes are randomly distributed throughout the 

 menstrual cycle. 



Shock : It seems to me that we have two possible interpretations of this 

 age reduction in intracellular water. The interpretation I favour is that 

 the reduction in total intracellular water is a reflection of the loss of 

 functional cells or the loss of protoplasm, rather than a change in the 

 water concentration of the remaining protoplasm. Have we any other 

 evidence that would make one interpretation more probable than the 

 other? 



Davson : I think that is a very sound point, because a cell can change in 

 size without there being a change in the relative value of the water or 

 solid contents of the organism. Is there any change in the histological 

 appearance of old tissue that would indicate whether the cells had be- 

 come smaller or larger? 



Shock : I cannot answer this question and must refer it to the patho- 

 logist or histologist. In our own work we have been looking for indices 

 of the total amount of man left functioning at a given age. Surface area 

 leaves much to be desired as a criterion, but one can account very nicely 

 for the age reduction in basal metabolism in terms of cellular loss if body 

 water is used as the index. In other words, although the basal metab- 

 olism per unit of surface area goes down with age, the basal oxygen con- 

 sumption per unit of intracellular water does not change at all with age. 

 When you try this with renal function data, renal plasma flow per unit 

 of body water goes down just as much as the renal plasma flow per unit of 

 surface area. 



Scribner: Total exchangeable potassium might possibly be a good 

 parameter for this measurement of protoplasm. 



