PHILOTHION. 559 



this enzyme has been observed by REY-PAILHADE (II. and VI.) in 

 various animal tissues and in germinating seeds. According to 

 Pozzi-EscoTT (V.), it is retained by the first-named cells during 

 the period of rapid reproduction, and is not diffused into the 

 nutrient medium until fermentation has culminated in the latter. 



ABELOUS and RIBAUT (I.) denied the existence of philothion 

 as such, and attempted to explain the above characteristic pro- 

 duction of sulphuretted hydrogen by referring to the capacity of 

 many proteids for readily parting with a portion of their sulphur 

 in that state of combination. Pozzi-EscoTT (III.), however, 

 demonstrated that the yeast extracts containing philothion lose 

 their power of producing this gas in abundance, on being boiled ; 

 which was soon afterwards confirmed by REY-PAILHADE (X.); 

 and that very energetic extracts are also able to reduce sulphites. 

 According to Pozzi-EscoTT (VI.) this enzyme affords the yeast a 

 means of defence against the poisonous action of sulphurous acid, 

 a statement, however, in direct conflict with the just previously 

 mentioned formation of that poison by philothion. Probably this 

 last worker was correct in his opposition to the assumption of 

 GIMEL (I.), who regarded oxydase as the protective agent, and 

 stated that yeast which has been habituated to large doses of 

 sulphurous acid (see p. 442, vol. ii.) is able to produce larger 

 quantities of oxydase than before habituation. 



On the basis of his observation that methylene-blue is a more 

 sensitive and rapid indicator than indigo-carmine, &c., for the 

 detection of reducing enzymes, H. HAHN (IV.) investigated more 

 closely the reducing power of expressed yeast juice. This power 

 disappears within a few days when the yeast has been stored in 

 the ice-chest in presence of toluol ; and almost entirely vanishes 

 on the juice being kept at 55-6o C. The optimum temperature 

 for reduction is 40 C., this agreeing with that (3o-4o C.) given 

 by Pozzi-EscoTT (VIII.). The reducing power is lowered by 

 diluting the yeast juice with water, whereas meat broth has a 

 favourable influence. The reduction proceeds most rapidly in old 

 yeast juice. The further observation of a certain parallelism 

 between the fermentative and reducing action of the juice recalls 

 the opinion held by J. Griiss on the part played by hydrogenase 

 (philothion) in alcoholic fermentation (see p. 488, vol. ii.), namely, 

 that it is the hydrogen temporarily formed during fermentation 

 (and not philothion) that acts on free sulphur. 



According to Pozzi-EscoTT (VIII.) the reduction is hindered 

 most powerfully by salts with an acid reaction mercury chloride 

 and silver nitrate in particular, the nitrates being rather less 

 injurious. Chloroform and acids retard, whereas alkalis stimulate 

 the action. 



More exhaustive investigations on the reducing power of yeasts 

 and the real cause thereof will not only increase the sum of our 

 knowledge on the theory of enzymes, but may be of practical 

 VOL. TI : PT. 2 2 N 



