430 SECOND CLASS OF MINERAL CONSTITUENTS. 



the observations of Brugnatelli, they at all events serve to explain 

 how it was that Brugnatelli and Treviranus were led to adopt this 

 view. For it is very possible that, as we always find small pebbles 

 and sand in the stomachs of these animals, a purely mechanical 

 attrition of the finest granules of sand may have apparently cor- 

 roded the pieces of agate and rock-crystal during their long sojourn 

 in the stomach, and thus have occasioned their loss of weight. 

 Moreover, I have never been able to detect any decided corrosion 

 of the pebbles which we find in the stomachs of ducks and fowls. 

 It would be strange if nature had here first ordained the secretion of 

 hydrofluoric acid, in order that it should immediately again disap- 

 pear through the action of the siliceous pebbles which are swallowed 

 by birds. Should not the hydrofluoric acid, if it were present, 

 expel other acids from the salts contained in the gastric juice ? 



CHLORIDE OP SODIUM. 



In almost every portion of the earth's surface we find this body 

 in all parts of the animal organism ; and it is not a mere incidental 

 constituent conveyed into the system with the food and drink, but 

 it is applied to definite, although highly various ends. 



The importance of chloride of sodium in the metamorphosis of 

 the animal tissues is illustrated by the fact that it always forms the 

 greatest part of the soluble constituents of the ash of all animal 

 substances. It is very constantly associated with certain animal 

 matters, and essentially influences their chemical and physical pro- 

 perties; thus albumen in part owes its solubility to the chloride of 

 sodium contained in it, and the differences which it presents in 

 coagulating are in part dependent on the quantity of this salt that is 

 present. Chloride of sodium dissolves pure casein, and has a sin- 

 gular power of impeding the coagulation of the fibrin of the blood. 

 If it is impossible to prove that chloride of sodium forms definite 

 chemical compounds with these bodies, the following considerations 

 at all events render such a view probable ; namely, the influence 

 this salt exercises on the above named protein-compounds, the 

 analogy of the compound of chloride of sodium and glucose, and 

 finally the impossibility, by mere washing, of perfectly separating 

 some of the protein-compounds from the chloride of sodium. 



We would especially refer the reader to the relation of albumen 

 towards salts, described in p. 332. 



In accordance with these facts we find that the chloride of 

 sodium, like other important constituents of the animal body, is 



