THE EFFECT OF AGE ON THE BODY'S 



TOLERANCE FOR FASTING, THIRSTING AND 



FOR OVERLOADING WITH WATER AND 



CERTAIN ELECTROLYTES * 



Nathan B. Talbot and Robert Richie 



Department of Pediatrics, Harvard Medical School and the Children's Medical 

 Service, Massachusetts General Hospital, Boston 



As is well known, the body is equipped with homeostatic 

 systems designed to maintain water and electrolyte content 

 and concentration values at physiologically optimal levels. 

 The systems accomplish this task largely by equating output 

 with input. While rates of input can be varied widely without 

 overreaching the capacities of the homeostatic systems con- 

 cerned, nonetheless there are limits beyond which one cannot 

 go without getting into difficulty (Talbot, Crawford and 

 Butler, 1953; Talbot et al., 1955). Thus for each substance 

 there is a physiological minimum requirement or floor, which is 

 the least intake of the substance in question needed to balance 

 output and hence to prevent deficits where conservation forces 

 are acting maximally. There is also for each substance a 

 physiological maximum tolerance or ceiling which is defined as 

 the largest amount of the substance that can be taken and 

 eliminated without seriously disturbing body composition. 

 Rates falling between these two parameters may be said to 

 fall within the physiological or safe working range. When the 

 rate of administration of a substance falls outside this range 

 for an appreciable length of time, body composition deviates 

 from normal and manifestations of disordered homeostasis 

 develop as outlined in Table I. 



* This paper is based on work supported by grant A-808 of the National 

 Institute of Arthritis and Metabolic Disease, by grants H-1529 and HTS 

 5139 of the National Heart Institute, United States Public Health Service, 

 and by a grant from the Commonwealth Fund of New York. 



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