884 METABOLISM. 
or on such vegetable food, e.g. rice, in which the potassium salts are 
only present in small quantity. It is further noteworthy that the 
peoples who live on an animal diet, without salt, carefully avoid a loss 
of blood when they slaughter the animals, for the blood contains a far 
larger amount of sodium in proportion to potassium than any other tissue 
or organ. The explanation of these facts is thus offered by Bunge 1 : — 
" The amount of salt which herbivorous animals take in with their food is, 
compared with the weight of the body, generally not much less than that 
consumed by carnivorous animals. On the other hand, there is a considerable 
difference in another constituent of the ash of their food, in the potassium. 
Herbivorous animals take at least three or four times as much of salts of 
potassium as the carnivora. This fact leads me to imagine that the abundance 
of potassium in vegetable food is the cause of the need for salt in the 
herbivora. If, for instance, a salt of potassium, such as potassium carbonate, 
meets with common salt or chloride of sodium in solution, a partial exchange 
takes place — chloride of potassium and carbonate of sodium are formed. Now, 
chloride of sodium is well known to be the chief constituent among the 
inorganic salts of blood plasma. When, therefore, salts of potassium reach the 
blood by the absorption of food, an exchange takes place. 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. 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 Common salt is therefore withdrawn from the 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." 
In confirmation of this deduction, Bunge found that the addition of 
potassium salts to his diet produced a striking increase in the excretion 
of chlorine and sodium. Thus 18 grms. of K 2 0, taken in the form of 
phosphate or citrate, caused the loss of an extra 6 grms. of chloride of 
sodium (as well as 2 grms. of sodium in other forms), about one-half of 
the common salt which is contained in the 5 litres of a man's blood. 
And 18 grms. of potash is an amount much less than may be introduced 
with many important articles of vegetable diet, such as potatoes, which 
contain 20 to 28 grms. K 2 in each 1000 grms. of dehydrated material. 
" Having regard to the important part which salt plays in the organism 
(as in the formation of the digestive secretion, or in dissolving the 
globulins), even a small diminution may be prejudicial to certain func- 
tions, and may give rise to the need of recovering the loss." 2 
There are two other constituents of the food which need special 
consideration, namely, iron and lime. 
The amount of iron which is egested is exceedingly small, and it 
may be expected therefrom that the amount present in the food 
under ordinary circumstances would also be small. Stockman has 
1 " Lectures," translated by Wooldridge, p. IIP. 
-Bunge, op. cit., p. 121. The student is referred to Bunge's original publications 
(''Lectures" and Ztsclir. f. Biol., Miinchen, 1874, Bd. x.) for a "full and very interesting 
discussion of this importaut subject. 
