38 INORGANIC FOODSTUFFS 



confirmation of von Bunge's interpretation of this phenomenon is 

 afforded by the custom of one tribe to which von Bunge refers, the 

 negro inhabitants of a region in the neighborhood of Khartoum. 

 These natives manufacture or formerly manufactured a salt of their 

 own, by igniting the ash of a plant belonging to Salsola or salt-wort 

 group. As has been stated, the majority of plants contain a much 

 larger proportion of potassium than of sodium. The plants of the 

 Salsola group are quite peculiar in the respect that their ash contains 

 a much higher proportion of sodium than of potassium. The employ- 

 ment of this particular plant-ash among all the others that might 

 have been tried can hardly be considered accidental, in other words 

 it must have been found to satisfy a desire not equally readily satisfied 

 by the ashes of other plants. 



The relation of a need for salt to the partaking of a vegetable diet 

 has had several peculiar historical consequences. For example, in the 

 Mosaic Law, the Jews are expressly commanded to present their 

 vegetable offerings to the Deity accompanied by salt. In Greek and 

 Roman times, sacrificial animals were offered up to the Gods without 

 salt, but the fruits of the earth with salt. 



The effect of eating salt with our food is therefore, to widen the 

 circle of palatable foods, We all know how insipid potatoes taste 

 without salt. That is probably attributable to their high content of 

 potassium, unusual even in plants. By adding salt to our diet we are 

 able to render potatoes palatable, and so with many more foodstuffs 

 of vegetable origin. 



So far, all of the facts which we have cited are in excellent harmony 

 with the view that a diet containing an excess of potassium salts gives 

 rise to a necessity and a desire for common salt. Not 'every animal 

 appears to experience this desire, however, for rabbits and hares, for 

 example, live on a diet containing an excess of potassium salts and yet 

 do not seek for salt and do not appear to experience any inconvenience 

 from lack of it. Domestic herbivorous animals will live without incon- 

 venience on a purely vegetable diet without salt indefinitely, although 

 they will eat salt when it is offered them and unmistakably find it 

 gratifying. None of these live on a diet so excessively rich in potassium 

 as potatoes, for example, but nevertheless there is no question but 

 that they must ingest a large excess of potassium salts. Yet the 

 blood-plasma of such animals remains of the usual composition, 

 containing an excess of sodium over potassium. 



Here we meet for the first time with a phenomenon which is of very 

 general occurrence in living matter, namely the phenomenon of selec- 

 tive assimilation by tissues. Living tissues, as we shall have occasion 

 to note many times, are not mere passive recipients of whatever may 

 be contained in the fluids which bathe them. They choose and select 

 suitable ingredients in suitable proportions and reject unsuitable or 

 excessive ingredients. A remarkable illustration of this is afforded by 

 an experiment of Landsteiner's. He fed young rabbits upon meadow 



