General Discussion 227 



potassium to normal (Schwartz, R., Cohen, J., and Wallace, W. M. 

 (1955). Amer. J. Physiol, 182, 39). 



Swyer: The sex difference in these responses to various hormones, 

 and other matters which must either themselves have a hormonal 

 basis or must be genetically determined, still puzzle me. What is 

 the true sex basis? Is it a question of androgens and oestrogens, or 

 the ratio of these two sex hormones, or is it in fact due to some 

 characteristic which depends upon the presence of one X or two 

 X chromosomes? 



Kennedy: It is probably something to do with species, but the 

 differences in size and growth between the castrate cockerel and the 

 castrate hen, and the same sort of thing in male and female castrate 

 rats, are very well known, and there is obviously a genetic difference 

 in the subsequent behaviour of the neonatal castrate. Some of the 

 early theories of ageing depended on body size, and one wonders how 

 much actual size, or organ development and growth as such, rather 

 than sex alone, affects the matter. The kidney of the male castrate 

 rat, even though it is castrated very young, is a much bigger organ 

 and in some senses, therefore, is a more developed or older organ than 

 that of a female rat. Purely structural factors may determine some of 

 the differences in what I think you call end-organ responsiveness. 



Swyer: Is castration even shortly after birth early enough? After 

 all, the foetal testis has a very important role to play and intra- 

 uterine castration might avoid this difficulty. 



Desaulles: That might possibly be helpful in determining the role 

 of the X zone. It is hard to imagine how the interrelationship be- 

 tween pituitary, adrenals and gonads acts just at the beginning of 

 life in the animal. 



Milne: Is the control to the castrate male a spayed female? 



Desaulles: They are quite different — that is the annoying point. 



Kennedy: When he discussed renal function Dr. Shock pointed out 

 that there was some similarity between the old and the young kid- 

 neys in their inability to sustain water diuresis and so on. It has been 

 shown (Smith, H. (1951). The Kidney; Structure and Function in 

 Health and Disease. New York : Oxford University Press) that if you 

 take an animal of intermediate age and remove one of its kidneys and 

 half the other, then the initial response, at least, is a great diminution 

 in water diuresis, which may take four weeks to be restored to about 

 two- thirds normal. This may suggest that the period during which 

 the major changes in the newborn develop is during the unfolding of 

 the anlage of the kidney ; senescence in most animals that have been 

 studied similarly involves a loss of structural units. So again, simply 

 the amount of end organ which is there may be the important thing, 

 apart altogether from what is called the endocrine climate. 



