SALT AND ITS PHYSIOLOGICAL USES. 567 



chain of argument. Therefore the principle of this theory is uncer- 

 tain and may be contested. Indeed, it has been. 



It is possible, contrary to the reasoning of Bunge, to increase the 

 relative and absolute quantity of potash taken into the system with- 

 out increasing the appetite for salt; indeed, we may even decrease the 

 desire for it. 



An example of this sort is found among the negro tribes of Africa 

 who use ll, mh salt." The use of this mineral condiment extends 

 throughout a large part of central Africa in the basins of the Ogove 

 and Sanga north of the Congo and in the provinces of the Free State 

 to the south on the opposite side of the river. The lack of sea salt 

 or rock salt causes these populations to replace this substance by 

 another saline material which they prepare on the spot by their own 

 means. 



But this is not ordinary salt — chloride of sodium; it is not even a 

 soda salt. They obtain this spurious salt from the ashes of plants. 

 Not the first that come to hand, for it is not immaterial what plants 

 are chosen for this purpose. On the contrary, they are carefully 

 selected species. They use particularly two plants from the river. 

 The favorite one is a floating aroid common on the Ogove and deter- 

 mined by M. Lecomte as the Pistia stratiotes. It is said that at cer- 

 tain places this plant is cultivated solely for the purpose of extracting 

 its salt. The second is a sort of high bamboo that grows in clumps 

 upon inundated banks. 



What peculiarity have these plants that causes them to be chosen to 

 the exclusion of others? We do not know. M. L. Lapicque, from 

 whom we have derived a part of this information, supposes that it is 

 the slight proportion of carbonates that the} 7 furnish when incinerated, 

 or as the effect of subsequent treatment. In a product destined for 

 food, the lack of alkaline carbonates is a decided advantage, for their 

 nauseous odor and alkaline taste is repulsive to all. 



After being harvested the plants are dried and then burned; the 

 ashes are collected and leached. At Berberati, on the Upper Sanga, 

 Dr. Herr witnessed this process. The aborigines use for this purpose 

 a rude filter made of a conical basket, in which the ashes are placed. 

 Through this water is passed and repassed several times to dissolve out 

 all the soluble salts. The solution thus obtained is then evaporated 

 by heat. The fixed residue forms the "ash salt." 



The composition of this salt, at least as to its general features, is 

 well known. M. Dybowski, in 1893, communicated to the Academy 

 of Sciences some analyses of it. Its composition varies little from 

 that furnished by most plants similarly treated. Normally, as has 

 been already said, potash is greatly in excess of soda in all vegetables. 

 The proportion varies from 30 to 150 parts of potash to 1 of soda. 

 That is what we find in this case; the quantity of soda is very minute. 



