990 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



liver, the normal action being either destruction in the liver itself or in other organs 

 through the medium of a substance (enzyme ?) produced in the liver. 



One may interpret Araki's experiment as showing that considerable quantities of lactic 

 acid are constantly produced in metabolism, but are normally swept away and burned ; the 

 CO-poisoning would prevent the normal combustion. The accumulation in muscle after 

 stoppage of blood-current (rigor mortis] would then be only a continuation of the normal 

 process of decomposition. 



Cystein, a-Amido-a-thiopropionic Acid. This substance has the formula 

 NH 2 



C COOH. It is a product of proteid metabolism and is normally 



destroyed in the body. On the introduction of a halogen derivative of benzol 

 into the body, compounds are formed with cystein, called mercapturic acids, 

 which appear in the urine: 



NH 2 NH 2 



CH 3 -C COOH + C 6 H 5 Br + O = CH 3 C COOH + H 2 O. 

 SH SC 6 H 4 Br. 



Bromophenyl-mercapturic acid. 



This proves that cystein (like glycocoll, for example) is at least an intermediary and 

 possibly a primary product of proteid metabolism (see p. 951). If cystein be fed, 

 the greater part (two- thirds) of the sulphur appears in the urine as sulphuric acid, 

 the rest as neutral sulphur. Thiolactic acid has been found 1 as a decomposition 

 product of horn. Baumann 2 demonstrates the reduction of cystein to thiolactic 

 acid, shows that the latter yields an odor of ethyl sulphide on evaporation, 

 and asks if thiolactic acid be not the mother substance of Abel's compound 

 (see p. 951) : 



NH 2 



CH 3 C COOH + H 2 - CH S CH(SH)COOH + NH 3 . 



Thiolactic acid. 



Cystein itself is never directly detected in the urine or in the body. 



Cystin, Dithio-diamido-ethidene Lactic Acid. Cystein is converted by 

 atmospheric oxygen into cystin : 



NH 2 



CH 3 CSNH 2 COOH 

 2CH 3 C COOH + 2O = I 



| CH 3 CSNH 2 COOH 



OTT 



Cystin. 



Cystin is very insoluble in water. In particular cases it appears in considerable 



1 Suter: Zeitschrlft fur physiologische Chemie, 1895, Bd. 20, p. 564. 



2 Baumann : Ibid., 1895, Bd. 20, p. 583. 



