Discussion 153 



tions of zero potassium intake. On the other hand, it was thought that a 

 thorough exposition of available information on these relations at this 

 time would serve only to confuse the picture without adding greatly to 

 its significance. Certainly one cannot take and eliminate large loads of 

 electrolyte without an ample supply of water etc. Accordingly, it was 

 decided to define physiological maximum tolerance and minimum require- 

 ment levels for each substance under circumstances where the influence 

 of these types of factors should be minimal, i.e. under conditions where 

 the rates of intake of substances other than the one under consideration 

 were well within normal limits. Should these preliminary definitions 

 prove to be of value, it may become worthwhile to undertake to extend 

 and refine them more by detailed definitions of certain of the most 

 important interrelations. 



You are correct in your deductions concerning our aims in defining 

 physiological key variables. The present definitions are of necessity ap- 

 proximate and potentially subject to modification and refinement. At 

 the same time they are pro\ang to be of value as indices of patient status 

 and as a point of departure for investigation. 



