226 NUTRITIONAL PHYSIOLOGY 



often true that there is any shortage in the amount offered 

 in the food. 



When the full stature is reached the need of a continued 

 salt income is less marked, though there is reason to believe 

 that the demand always exists. A certain loss in the urine 

 and through the skin seems bound to occur, though the 

 usual excretion of salts is far greater than the bare mini- 

 mum, and appears to indicate a needless excess in the in- 

 come. The salts of the diet have much to do with its 

 palatability and so deserve a place with the organic condi- 

 ments. An unusual quantity of saline matter may be sup- 

 posed to impose a hard task upon the kidneys, and is 

 known to aggravate any dropsical tendency that may be 

 present. 



Sodium chlorid is the one salt which we take pains to 

 secure. We are inclined to think of it as a mere relish, 

 but it has been shown that it has a deeper significance. 

 The Austrian physiologist Bunge has found that it is 

 sought both by animals and men whose food is largely or 

 entirely vegetable. It is repugnant to those that are ap- 

 proximately carnivorous. Bunge points out that vegetable 

 foods are generally rich in compounds of potassium and 

 relatively deficient in those of sodium. He has demon- 

 strated that when an excess of potassium salts is eaten 

 the kidneys discharge the foreign material promptly, and 

 in doing so let slip a good deal of the sodium chlorid from 

 the blood. Accordingly, it is inevitable that the steady 

 consumption of foods rich in potassium should create a 

 demand for sodium. The seeking of common salt to meet 

 the need is a singular illustration of the almost unerring 

 working of instinct. 



