Discussion 207 



deer? Deer may have sickle cells, and this is correlated with a certain 

 type of different haemoglobin. 



Davson: I know the camel has ellipsoidal cells. 



Bull : Is anything known about the relative efficiency of the different 

 kinds of red cells with respect to their function of carrying oxygen, in 

 relation to pH changes, carbon dioxide changes, etc. 



Karvonen : Quite a lot is known about species and foetal-adult differ- 

 ences, but nobody has studied these aspects within one species, and at 

 the same time paid attention to the intra-species variations in intra- 

 cellular electrolytes. 



Hingerty : It seems from the last three papers that there may be some 

 sort of late development of function as regards sodium and potassium 

 control. It may be something, according to Dr. Desaulles's work, that 

 develops in the rat at about 5-6 weeks, or something that increases the 

 efficiency of sodium — potassium exchanges across the cell membranes, 

 or the reabsorption rates in the renal tubules. During our potassium- 

 depletion experiments we found that in young rats up to six weeks of age 

 we could replace about 25 per cent of the muscle potassium by sodium on 

 potassium-deficient diets (Conway, E. J., and Hingerty, D. J. (1948). 

 Biochem. J., 42, 372). When we repeated the experiment we happened to 

 use rats of about nine or ten weeks old, and we found that the exchange 

 rates were much lower. Probably a greater efficiency develops in the 

 interval ; either the cell holds on to the potassium more efficiently or the 

 sodium pump works more efficiently. Possibly these changes are gradu- 

 ally developing in the growing animals and their responses to hormones 

 may also develop gradually. 



Shock : One of the problems that occurred to us was whether the eryth- 

 rocytes that are formed in the normal course of turnover in the very old 

 individual can act as effectively as those in the young individuals. We 

 have not yet done the obvious experiment of producing a stress which 

 causes haematopoiesis, but we have examined the osmotic fragility of 

 red cells from individuals between the ages of 20 and 90, with about 

 ten individuals in each decade. With careful control of the pH, which 

 influences the fragility rather markedly, we found no striking evidence 

 of differences in the osmotic resistance of red cells taken from individuals 

 as old as 90, as compared with the young individual. 



I also wonder whether there are subtle differences between the chemi- 

 cal structure of haemoglobin formed in an old individual as compared 

 with that in the young or middle-aged person. If the haemoglobin from 

 80-90-year-old individuals had been subjected to as detailed and careful 

 an analysis as that which resulted in the identification of the different 

 types of haemoglobin in the foetus, perhaps we would have found that 

 differences appear after a lifetime of utilizing the mechanism for making 

 haemoglobin. 



McCance : Dr. Davson, can you comment upon the genetic side of this? 

 You spoke about the sodium pump ; what about the difference in haemo- 

 globin? 



Davson: I cannot relate this at all. I do not see why a given type of 

 haemoglobin should be associated with a given electrolyte content. 



