44 PHYSIOLOGY CHAP. 



being extraneous to the plasma, are eliminated by the kidneys, 

 thus causing an increase in the potassium and sodium in the urine. 

 Hence the blood becomes poorer in chlorine and in sodium, 

 and the necessity arises for the addition of sodium chloride to 

 vegetable foods. 



It has been objected to Bunge's doctrine that certain negro 

 tribes in Africa use the salt of ashes instead of ordinary cooking 

 salt ; this so-called salt of ashes is obtained by reducing certain 

 plants to ashes and treating them in such a way as to deprive 

 them almost entirely of alkaline carbonates, so that what remains 

 is composed almost entirely of chloride of potassium with a small 

 quantity of chloride of sodium. It tastes much like ordinary 

 cooking salt ; the negroes are extremely fond of it and prefer it to 

 ordinary salt. Without accepting Bunge's theory as absolutely 

 correct, we can still hold that the excess of potassium salts intro- 

 duced takes with it during elimination by the kidneys sodium 

 chloride from the plasma, and thus induces this need for the addition 

 of salt to the food (Zuntz). 



There is a larger quantity of potassium than sodium in the milk 

 of herbivorous animals, and also in human milk, a fact which shows 

 that a slight preponderance of potassium in the food is allowable. 

 In meadow hay there is also only a slight preponderance of 

 potassium, and this accounts for herbivorous animals, such as 

 rabbits and hares, eating it readily without the addition of salt. 

 A diet consisting only of vegetables which contain a large quantity 

 of potassium, such as clover, affords an example of the need of 

 salt. Herbivorous domestic animals which feed on such plants 

 improve in condition if given rock salt, and suffer if they are 

 deprived of it. 



Man can live on a vegetarian diet without salt, if he avoids 

 those foods which contain a great deal of potassium, such as 

 potatoes, rye, peas, and beans. Country people use much more 

 salt than townsfolk, in France three times as much, because they 

 live mainly on potatoes and vegetables, whereas the inhabitants 

 of towns take more bread, wine, and meat. 



As a general rule, the evidence shows that there is generally an 

 excessive use of cooking salt, more undoubtedly than is strictly 

 necessary ; it serves at the same time as a condiment, giving 

 flavour to the food, and thus stimulating the sense of taste and 

 the secretion of the digestive juices. 



The excessive use of salt as a condiment is however undesir- 

 able, for it imposes upon the kidneys an abnormal amount of work. 



According to Voit's researches the lavish use of sodium chloride 

 causes an increase of about 5 per cent of nitrogen in the urine ; 

 this effect is however due not to an increased consumption of 

 albumen, but to the fact that the salt, by taking water from the 

 tissues, causes an increased flow of urine and hence a more rapid 



