14 INTRODUCTION. 



us a sufficient explanation of the oxidative processes in the animal body, 

 and the various divergent views as to the nature of these show us 

 strikingly how little is positively known about these processes. There 

 is no doubt that the animal body possesses in the so-called oxidation 

 enzymes important means of bringing about oxidative decomposition 

 cf various substances, and the occurrence of numerous intermediary 

 metabolic products in the animal body teaches us that the oxidation of 

 the constituents of the body is not instantaneous and sudden, but takes 

 place step by step, and hand in hand with cleavages. For a long time 

 the oxidations in the animal body have been considered as a combus- 

 tion, and such a conception is easily reconcilable with the above-men- 

 tioned views. In combustion in the ordinary sense, as, for example, 

 the burning of wood or oil, we must not forget that the substances 

 themselves do not combine with oxgyen. It is only after the action of 

 heat has decomposed these bodies to a certain degree that the oxidation 

 of the products of such decomposition takes place and is accompanied 

 by the phenomenon of light. The above-mentioned specificity of the 

 oxidation enzymes and also the recent observation that indeed rather 

 simple cleavage products are burnt with difficulty in the organism and 

 also that of two optical antipodes of an amino-acid, for example of leucine, 

 the one (Z.-leucine) is readily burnt while the other (d-leucine) is burnt 

 with difficulty and only incompletely, seem to make it very probable that' 

 in many cases a very intense cleavage is necessary before oxidation occurs. 



Most investigators are agreed that these decompositions are similar 

 to certain oxidations studied by DRECHSEL 1 outside the animal body, 

 where oxidations and reductions alternate in quick succession. The views 

 are divided in regard to the manner and origin of this cooperative action. 2 



As the oxidations are explained by the action of special enzymes, 

 so also special reducing enzymes, so-called reduclases or hydrogenases, 

 have also been accepted. Certain investigators claim that the so-called 

 philothions, which develop hydrogen sulphide in the presence of sulphur 

 and water, belong to this group, while others, on the contrary, do not 

 accept this view, but consider the enzymotic nature of the philothions 

 as doubtful. 3 The investigations of NASSE and ROSING 4 on the oxi- 



1 Journ. f. prakt. Chem. (N. F.), 22, 29, 38, and Festschrift fiir C. Ludwig, 1887. 



2 See M. Nencki, Arch, des sciences biol. de St. Pe"tersbourg, 1, 483; Abelous and 

 Aloy, Compt. rend., 136, 137; Kastle and Elvove, Amer. Chem. Journ., 31; Underhill 

 and Closson, Amer. Journ. of Physiol., 13. 



3 De Rey-Pailhade, Recherches expe"r. sur le Philothion, etc., Paris (G. Masson), 

 1891, and Nouvelles recherches sur le Philothion, Paris (G. Masson), 1892; Bull. soc. 

 chim. (4) I; Pozzi-Escot, Bull. soc. chim. (3), 27, and Chem. Centralbl., 1904, 1, p. 

 1645; Chodat and Bach, Ber. d. d. chem. Gesellsch., 36; Abelous and Ribaut, Compt. 

 rend., 137, and Bull. soc. chim., Paris (3), 31. 



4 See footnote 2, p. G. 



