566 TISSUE RESPIRATION 



the physiological function of which he supposed to consist 

 in the reduction of oxygen coming into the tissues into 

 water. 24 



All these observations have, however, appeared in an 

 entirely new light since Heffter 25 subjected them to syste- 

 matic study. It was shown that certainly in large part the 

 phenomena which are connected with the autoxydizability 

 and reducing power of protoplasm are occasioned by the 

 presence of sulphydril groups (SH). The beautiful violet 

 color struck by sodium nitroprusside with alkali sulphides 

 may be traced to the sulphydril groups. Arnold was able 

 to show that a number of proteins give the reaction, and 

 that it can also be due in tissue extracts no longer containing 



CH 2 .SH 



protein by the presence of cystein, 26 CH.NH 2 . The nature of 



COOH 



the changes and the mode of action by which sulphydril 

 groups react with oxygen is illustrated in the autoxidation of 

 thiophenol (C 6 H 5 .SH), which takes up oxygen when shaken 

 with air, peroxide of hydrogen being produced as an inter- 

 mediate material. 27 Heffter would represent the reaction of 

 the sulphydril groups in the tissues accordingly by the fol- 

 lowing schema : 



R S R s 



2R.SH + O 2 = I + H 2 O 2 ; 2R.SH + H 2 2 = | + 2H 2 O. 



R-S 



It is possible to fancy that the transformation of cystein 

 into cystin (occurring spontaneously and at low tempera- 

 ture) may perhaps take place in this manner. 



84 Of. also D. F. Harris (Birmingham), Biochem. Jour., 5, 143, 1910; A. 

 Montuori, Memoirie della Soc. ital. delle Scienze, serie III, 16, 237, 1910; ArcTi. 

 ital. de Biol., 55, 197, 1911. 



25 A. Heffter, 1. c., and Hofmeister's Beitr., 5, 213, 1904; Arch. f. exper. 

 Pathol., Schmiedeberg Festschr., 253, 1908; B. Strassner (Heffter's Lab.), 

 Biochem. Zeitschr., 29, 295, 1910. 



26 V. Arnold (Lemberg), Zeitschr. f. physiol. Chem., 70, 300, 314, 1911. 

 " According to Engler and Broniatowski. 



