PHYSIOLOGICAL OXIDATIONS. 961 



do not affect the living tissue itself. They take place under the 

 influence of the living matter, or by the aid of substances (enzymes) 

 formed by the living matter, but the material actually burnt is not 

 organized living substance. As the living yeast cells break down 

 sugar in the liquid surrounding them, so the living tissue cells metab- 

 olize and oxidize the dead food material contained in the lymph 

 and tissue liquid in which they are bathed. The opposite point of 

 view was ably advocated by Pfliiger. This observer, in fact, ex- 

 plained the mystery of physiological oxidations by assuming that 

 the oxygen together with the food material is synthesized into the 

 highly complex and unstable living molecules. The active intra- 

 molecular movement within these molecules leads constantly to a 

 breaking down, a splitting off of simpler molecules which consti- 

 tute the products of physiological oxidation. The instability of 

 the molecule is due to its size and the activity of the intramolecular 

 movements, or, as Pfliiger expressed it, "The intramolecular heat 

 of the cell is its life." This point of view, however, has not found 

 acceptance of late years. It is implied or stated by most recent 

 authors that the food material is attacked and oxidized outside the 

 living molecule, in the form of fat, sugar, protein, or rather in the 

 form of the intermediary products arising in the metabolism of 

 these substances. The tendency for many years has been to show 

 that these processes in the body are chemical changes that do not 

 differ fundamentally from similar processes outside the body. 

 The point of view actually adopted by most workers is that the 

 living matter effects its wonderful changes in the food material by 

 making use of intracellular ferments or enzymes (endo-enzymes).* 

 That such enzymes are formed, one may say, generally in the tis- 

 sues of the body, has been brought out in the preceding chapters, 

 upon Digestion and Nutrition. It is necessary only to recall the 

 facts that lipase, the fat-splitting enzyme, has been isolated from 

 many tissues, and that in the liver and muscles and probably other 

 tissues there exist enzymes capable of converting glycogen to sugar 

 or the reverse, and of oxidizing the sugar completely by the serial 

 action of several intracellular enzymes. Finally, with regard to the 

 protein material, it is now recognized that proteolytic enzymes are 

 formed within many, if not all, of the living tissues. This point is 

 demonstrated by the fact of autolysis, that is, if living tissue is 

 taken from the body, with precautions against contamination by 

 bacteria, and while under perfect aseptic conditions is kept warm 

 and moist, it will digest itself. The protein is split up into the same 

 simple hydrolytic products as are obtained by boiling it with 

 acids. It has been shown that this digestion is due to enzymes 

 autolytic enzymes formed within the living tissue. There is no 



* For literature, see Vernon, "Intracellular Enzymes," London, 1908. 

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