86 



hade,^^ who in 1888, announced that in beer yeast he had found a 

 substance which caused the evolution of hydrogen sulphide from 

 sulphur, even in the cold. In the potato, egg-plant, etc., Kastle 

 and Elvolve^^ found that there were substances which reduced 

 nitrates to nitrites, the most favorable temperature for this 

 action being from 40° to 50°; the action being retarded by acids 

 and much increased by benzaldehyde and benzyl alcohol. Action 

 is also completely checked by boiling, but the authors hesitated 

 to say that this action is due to an enzyme; they classified this 

 reducing substance with those compounds that are unstable and 

 easily oxidized, and which reduce nitrates, but not in unlimited 

 quantity. This statement might also be applied to the so-called 

 reducing enzymes found by Irving and Hankinson^® in the 

 Gramineae. In the action of both yeast and bacteria, reduc- 

 ing substances probably play a part, since they are usually 

 present. 



We may say, then, that reducing substances are of common 

 occurrence in plants, both in the higher and lower representatives. 

 In many plant juices there occur reducing substances which, 

 in the test for oxidases with the color reagents, gradually de- 

 colorize all the mixture except a zone near the surface of the 

 liquid; this upper colored part being immediately bleached if 

 the solution is thoroughly shaken, but it reappears upon standing. 

 These reducing substances, as well as catalase, may act as a 

 check upon the activity of peroxidase in the living cell, but 

 after death or narcosis, the production of reducing substances 

 is lessened and the oxidases develop pigments, i. e., oxidize 

 the chromogens to colored compounds. It seems doubtful that 

 these reducing substances are enzymes, since we know that 

 ordinary reducing substances resulting from metabolism are 

 present in practically all animal and plant cells. Such substances 



3''Rey-Pailhade: (a) Nouvelle recherche physiologique sur la substance organique 

 hydrogenant le soufre a froid. Compt. Rend. Acad. Sci. 107: 430. 1888. (&) Sur 

 une corps d'origine organique hydrogenant le soufre a froid. Compt. Rend. Acad. 

 Sci. 106: 1683. 1888. 



^Kastle and Elvolve. The Reduction of Nitrates by Certain Plant Extracts, 

 etc. Am. Chem. Jour. 31: 606. 1904. 



'^ Irving and Hankinson. The Presence of Nitrate Reducing Enzymes in Green 

 Plants. Biochem. Jour. 3: 87. 1908. 



