140 



Nathan B. Talbot and Robert Richie 



The manner in which a hmit to homeostatic capacity can 

 be recognized and defined is illustrated in Fig. 1 (Talbot et al., 

 1956). Here it can be seen that this patient maintained a 

 normal potassium status, as judged from electrocardiographic 

 T waves and from serum potassium concentration, and 

 remained in potassium balance at rates of intake up to 

 approximately 70 m-equiv. per m.^ per day. These rates of 



Table I 



Indications that intake is physiologically excessive or insufficient 



(adult values) 



Nas = extracellular sodium. 



Ki = intracellular potassium. 



Corrected for urea. 



intake could therefore be considered to be within his safe 

 working range. By contrast, higher rates of intake led to a 

 sustained positive balance and to the appearance of elevated 

 T waves and hyperkalaemia, which are taken to be signs of 

 potassium intoxication. Accordingly, it may be said that this 

 individual's ceiling of tolerance for potassium was about 

 70 m-equiv. per m.^ per 24 hours, a subnormally low value in 

 comparison with a normal ceiling of at least 250 m-equiv. per 

 m.2 and in keeping with the fact that he was suffering from 

 marked impairment of renal function. 



