METABOLISM 179 



are burned and are therefore spoken of as ash ingredients, al- 

 though, as already pointed out (3, 5), this does not necessarily 

 imply that they existed in the original material in " inorganic " 

 combination. Most of these elements are as essential to the 

 vital processes as the more abundant elements carbon, nitro- 

 gen, hydrogen and oxygen of the so-called " organic compounds," 

 although unfortunately the laws regulating their metabolism 

 have been much less extensively studied. Among these ele- 

 ments sulphur and phosphorus are of special importance in 

 this connection. 



Sulphur 



255. Sources. While feeding stuffs may contain small 

 amounts of sulphur in the form of sulphates, by far the greater 

 part of this element in the feed of animals exists in organic 

 compounds. Such, for instance, are the allyl sulphid (CsHs^S, 

 contained in garlic and other members of the genus allium, and 

 the allyl sulphocyanat, CsHs CNS, found in mustard and other 

 genera of the cruciferae. Ordinarily, however, the chief car- 

 riers of organic sulphur, both in feeding stuffs and animals, 

 are the proteins, which contain the element in the form of the 

 di-amino acid cystin (47). 



256. Katabolism. The question whether the animal body 

 can build up its sulphur compounds from inorganic sulphur 

 does not appear to have been investigated. 



The katabolism of the cystin component of proteins pre- 

 sumably follows the same general course as that of the other 

 amino acids, i.e., it is split off from the proteins by hy- 

 drolytic cleavage and subsequently deaminized. One of the 

 products of. the katabolism of cystin appears to be taurin, 

 CH 2 NH 2 CH 2 SOsH, contained in the taurocholic acid of the 

 bile. To the extent, therefore, to which the latter com- 

 pound escapes resorption in the lower intestine, it carries small 

 amounts of sulphur into the feces. Both cystin and taurin, 

 however, are readily oxidized in the body, the larger part of 

 their sulphur taking ultimately the form of sulphuric acid and 

 being excreted in the urine. The sulphuric acid of the urine 

 exists in combination in part with aromatic radicles derived 

 from the putrefaction of the proteins in the lower intestine 

 and in part with bases. In human urine about one-fifth of 



