REDUCING TISSUE COMPONENTS 565 



" physiological " conditions, using, besides physiological 

 salt solution, also blood serum and blood itself. In this case 

 respiration was less marked in homologous serum than in 

 physiological salt solution. After extirpation of the kidneys 

 substances are thought to accumulate in the blood having 

 an unfavorable influence upon the tissue respiration. 21 



Reducing Tissue Components. Another group of phe- 

 nomena usually regarded as connected with the processes of 

 tissue respiration involve the reducing power of tissues and 

 tissue constituents. 



Paul Ehrlich, in the course of his studies of the oxygen 

 requirement of the body, injected methylene blue into ani- 

 mals. This coloring material is changed by reduction into 

 its leukocombination ; by oxidation the latter may be re- 

 turned into the original dye. It may be easily noted in the 

 animals thus injected with methylene blue in which of the 

 tissues the blue dye has retained its color and in which it 

 has been decolorized, to be restored when atmospheric air 

 gains access to it. The reduction of the methylene blue in 

 the tissues can be followed by titration with titanium 

 chloride. 22 A number of other examples of reducing actions 

 have been met from time to time in the body ; as the reduc- 

 tion of nitrates to nitrites, of arsenic acid to arsenious acid, 

 of nitrobenzol to aniline, of iodates to iodides, of tellurates 

 to tellurium, of sulphur to sulphuretted hydrogen, etc. 23 



Such reductions have been looked on by many authors as 

 predicating the existence of reducing ferments (reductases). 

 Thus deRey-Peilhade ascribed the reduction of finely emulsi- 

 fied sulphur into sulphuretted hydrogen, which a number of 

 tissues are capable of inducing, to a ferment, "philothion," 



21 F. Lussana (Bologne), Arch, di Fisiol., 6, 269, 1909; 8, 239, 1910; 9, 575, 

 1911. 



22 H. Wichern (Leipzig), Zeitschr. f. physiol. Chem., 57, 365, 1908. 



23 Literature upon Reducing Actions of the Tissues: A. Heffter, Mediz. 

 naturw. Arch., 1, 82-103, 1907; T. Tunberg, Ergebn. d. Physiol., 11, 328-344, 

 1911. 



