132 W. M. Wallace, W. B. Weil and A. Taylor 



with age the maximum change of water content is no more 

 than 1 per cent and of potassium 5 per cent. 



Examination of whole body data, with certain saHent ex- 

 ceptions, also shows rather remarkable constancy. Fat is 

 probably the only component of the total body that can vary 

 within rather wide limits and still allow reasonable well-being 

 to exist. Variation from 10 to 50 per cent can occur without 

 apparent evidence of malfunction. The water content of the 

 fat-free body is more closely guarded. Variation of much 

 more than i- 5 per cent from a rather rigid norm results in 

 rapid increments of physiological disability. Moreover, 

 allowable variation of body water is primarily extracellular; 

 cellular water content, within the limits of viability, must be 

 confined to much smaller variations. Since protein is the 

 critical parameter against which water content must be 

 judged, it follows that protein concentration must also be 

 highly critical and susceptible to only minute variation. The 

 consideration applying to water must also hold for the chief 

 extracellular electrolytes, sodium and chloride. Deficit of 

 potassium in the whole body to the extent of approximately 

 25 per cent does occur, and is replaced by variable gains of 

 total body sodium (Schwartz, Cohen and Wallace, 1953; 

 Cheek and West, 1956). The studies of Sherman and Booher 

 (1931) show that the calcium content of the whole body is 

 widely variable in response to variation in the dietary intake. 

 Definition of the optimal body content of this ion is elusive. 



In the discussion so far the point of view has been taken that 

 in order to justify the terms stored protein or mineral, these 

 must exist as physically demonstrable entities comparable to 

 glycogen and fat in the body. It would appear that the 

 essential organic structure of the body cannot be affected in 

 quality by adjustment of the diet. The careful chemical 

 analyses by Luck (1936) of rat liver proteins from animals 

 maintained on varying levels of protein intake indicate that 

 all fractions of the liver proteins have participated equally 

 in any "storage" process. Madden and Whipple (1940) have 

 defined the reserve store of protein as "... all of the protein 



