FUNCTIONS OF MINERAL SUBSTANCES. 13 



chlorin, iodin, fluorin, carbon, hydrogen, nitrogen, oxygen, sulphur, 

 and silicium. 



VARIETY OF FUNCTIONS OF MINERAL SUBSTANCES. 



A question of fundamental importance is whether a certain mineral 

 constituent has one or several functions to perform, and in the latter 

 case whether at least one of these several functions may not be per- 

 formed by some other related constituent — in other words, whether a 

 partial substitution in the organisms would be possible. When a mere 

 neutralization of acids or an osmotic action is involved there can be no 

 doubt that potash or lime may be replaced by soda, or when incrus- 

 tation of a tissue is necessary for protection the place of calcium car- 

 bonate might betaken even by silica. The solution of various mineral 

 salts produces osmotic pressure and motion required also by animals. 

 Thus beef tea containing 0.85 gram of salts per liter exerts an osmotic 

 energy of several atmospheres, of which, however, only about one- 

 fourth can be realized in the stomach, since the blood itself also con- 

 tains mineral salts. However, it suffices to produce an aqueous current 

 from the blood to the stomach, while in the intestines the current takes 

 the opposite direction." Such functions are not specific, however. 

 In the purely physiological functions of a chemical nature not even 

 a partial substitution is possible, notwithstanding that various asser- 

 tions have been made to the contrary. In the living protoplasm potas- 

 sium can just as little be replaced by sodium as carbon by silicium. 



There exist physical and chemical functions, as well as ecological and 

 physiological roles. A further distinction may be drawn between 

 elements absolutely necessary and such as act merely beneficially. 

 Sodium, manganese, and silicium in the phanerogams belong t< > the latter 

 group. A physical function is performed by the calcium phosphate 

 in the bones, by the silica in the shells of Radiolaria and Diatomese, 

 and the calcium carbonate in those of Foraminif&rse, mollusks, and 

 birds 1 eggs. The protection against snails afforded to certain leaves by 

 the needle crystals of calcium-oxalate is an example of an ecological 

 role, as is also the free sulphuric acid secreted by certain Gastropoda, 

 as Dolium and Cassis. 



In order to furnish a foundation upon which to base a theory of the 

 special functions of the various mineral constituents, separate analy- 

 ses for each kind of organ are indispensable. In former times entire 

 plants or animals were subjected to incineration and the ash analyzed, 

 but such results were of very restricted value. 6 



« Koppe, Therap. Monatshefte, 1897. 



''Thus one author has inferred from his analyses that there is less magnesia in cats 

 than in dogs and less potash in dogs than in rabbits. (Zeitschr. f. Biologie, Vol. 

 X,p.321.) 



