It is claimed that the abundance of potassium salts in vegetable foods is the cause of the apparent need for sodium chloride by herbivorous animals, and in lesser degree by man. This is explained by supposing that when the salts of potassium reach the blood by absorption of the vegetable foods, an interchange takes place with the sodium chloride of the blood plasma. “Chloride of potassium and the sodium salt of the acid which was combined with the potassium are formed. Instead of the chloride of sodium, therefore, the blood now contains another sodium salt, which did not form part of the normal composition of the blood, or at any rate not in so large a proportion. A foreign constituent or an excess of a normal constituent, _i. e._, sodium carbonate, has arisen in the blood. But the kidneys possess the function of maintaining the same composition of the blood, and of thus eliminating every abnormal constituent and any excess of a normal constituent. The sodium salt formed is therefore ejected by the kidneys, together with the chloride of potassium, and the blood becomes poorer in chlorine and sodium. Common salt is therefore withdrawn from the organism by the ingestion of potassium salts. This loss can only be made up from without, and this explains the fact that animals which live on a diet rich in potassium, have a longing for salt” (Bunge). It is certainly a fact worthy of note that man takes only one salt as such in addition to those that are naturally present in his food, and it is equally significant that sodium chloride is by no means lacking in ordinary foodstuffs. If the individual lives entirely on animal foods, he has no desire for salt, but as soon as he adopts a vegetable diet the craving for salt shows itself. Vegetable foods, however, are not all alike in their content of potassium salts; some, like rice, contain relatively little, while others, like potatoes, peas, and beans, are comparatively rich in this element.