REDUCTIONS. 15 



elation of protein in the presence of sulphur, speak against the enzymotic 

 nature of this formation of hydrogen sulphide and the recent investi- 

 gations of HEFFTER 1 have shown that certain reductions occurring in 

 the tissues cannot be produced by enzymes. He has shown that those 

 reductions which are not influenced by HCN, such as the reduction of 

 pigments (methylene blue) can be brought about by the unstable H of 

 sulphhydric compounds. For example, cysteine (see Chapter III), which 

 quickly reacts with sulphur with the formation of H 2 S, acts in this manner, 

 and he has also shown the presence of similarly acting substances in 

 various organs and organ extracts. Here we have a group of reductions 

 which are not enzymotic. The reduction of nitrates seems at least in 

 part, according to the investigations of VoGELSOHN, 2 not to be brought 

 about by enzymotic substances. 



There is no doubt that reductions occur to a great extent in the 

 animal body and often hand in hand with oxidations; nevertheless the 

 question as to how far special reduction enzymes take part in these reduc- 

 tions is still an open one. According to ABELOUS and ALOY 3 we have 

 indeed enzymes that have an oxidizing as well as a reducing action, 

 for they obtain the oxygen necessary for the oxidation of one body by 

 removing it from another substance through reduction. Still this question 

 requires further study. 



The essential source of heat and mechanical work developed in the 

 organism is to be found in the oxidations. Chemical energy is trans- 

 formed into the above-mentioned forms of energy in cleavage processes, 

 where complicated chemical compounds are reduced to simpler ones, 

 and therefore the atoms change from an unstable to a stabler equi- 

 librium, and stronger chemical affinities are satisfied. The animal body 

 may also have a source of energy in the cleavage processes which are not 

 dependent on the presence of free oxygen. The processes taking place 

 in the active muscle are examples of this kind. A removed muscle, 

 which gives off no oxygen when in a vacuum, may, as HERMANN 4 has 

 shown, work, at least for a time, in an atmosphere devoid of oxygen, 

 and give off carbon dioxide at the same time. 



The cleavage processes are not only of especially great importance 

 for the digestion of the foodstuffs and for their availability for the 

 animal body, but also are important for the metabolic processes. If 



1 Mediz. naturw. Arch., 1, p. 81-104, Marburg; cited in Chem. Centralbl., 1907, p. 

 822. 



2 Ueber die Einwirkung von Organextrakten auf Nitrate und Nitrite, Inaug.- 

 Dissert.. Bern, 1907. 



3 Compt. rend., 136, 137 and 138. See also Abelous and Gerard, ibid., 129, on fhe 

 reductaaes; Pozzi-Escot, Bull. soc. chim. (3), 27. 



4 Untersuch. iiber den Stoffwechsel der Menschen, Berlin, 1867. 



