ELEMENTS OF COMPOSITION. 55 



p"M- \ 



Sulphocyanide of potassium (rhodanide of potassium), -r/ > S , is the 



only cyanogen compound met with in the human economy, and that in 

 extremely small quantity. It is a constituent of saliva, in which it was 

 discovered "by Treviranus ; its occurrence here, however, is not without 

 exception. 



The origin and relations of this compound are still entirely unknown. 



Sulphocyauide of potassium gains in interest, moreover, when we remem- 

 ber that in the physiological mutation series no other cyanogen combina- 

 tions make their appearance. 



L. Mineral Constituents. 



39. 



The number of mineral substances and inorganic compounds occurring 

 in the human body is not inconsiderable. Our knowledge of these, how- 

 ever, is unfortunately far less perfect at present than the nature of the 

 substances in question might lead us to expect. In respect to the com- 

 bination of inorganic matters, we are so far as the question turns upon 

 their pre-existence in the various parts of the body, or to what extent 

 they must be regarded as only produced by chemical manipulation itself 

 by no means as clear as might be desired. But greater obscurity still 

 prevails in regard to the physiological relations of some of these substances. 

 Granting, for instance, that no doubt can exist that in water we have 

 before us the chief solvent and agent in saturation and gelatinization of 

 the system, and that phosphate of calcium constitutes the most important 

 hardening medium of the same, and so on, there remains still a consider- 

 able number of substances whose purposes in the body we are unable to 

 ascertain with anything like certainty. It is likewise beyond our power 

 at present to distinguish with precision between those inorganic com- 

 pounds which occur as decomposition products in the economy, and those 

 which possess histogenic properties. Finally, there are in all probability 

 many mineral matters in the system which are only casual constituents of 

 the same, introduced with the food. 



It would lead us too far to detail here all the differences in' amount 

 between the ash constituents of the several tissues and organs of the 

 body. The variation in this respect, according to age, is of such great 

 interest, however, that a few points may be noticed in regard to it. 



While, in the earlier periods of foetal life, the ash only amounts to 1 

 per cent, of the whole weight of the body, it rises later on to 2, and reaches 

 in mature mammals so high as 3*5, 4, or even 7 per cent. In advanced age 

 it is probable that this is still further increased (Bezold and Schlossberger). 



Among the inorganic matters and compounds found in the body, the 

 following must be specially borne in mind : 



(a.) Gases oxygen, nitrogen, and carbonic acid. 



(b.) A cidsr- carbonic, phosphoric, sulphuric, hydrochloric, hydrofluoric, 

 and silicic. These, with the exception of the carbonic acid, diffused through 

 fluids, and hydrochloric acid, found free as a constituent of the gastric 

 juice, hardly ever occur in a free state in the body, but almost invariably 

 combined with bases. 



(c.) Bases potash, soda ammonia, lime, magnesia, oxides of iron, man- 

 ganese (and copper). These usually appear as salts, and yet we have free 

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