868 NUTRITION AND HEAT REGULATION. 



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, etc. The ten- 

 dency 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 won- 

 derful changes in the food material with the aid of intracellular 

 ferments or enzymes. That such enzymes are formed, one may say 

 generally in the tissues of the body, has been brought out in the pre- 

 ceding chapters upon Digestion and Nutrition. It is necessary" only 

 to recall the facts that lipase, the fat-splitting enzyme, has been iso- 

 lated from many tissues, and that in the liver and muscles and prob- 

 ably other tissues there exist enzymes capable of converting glycogen 

 to sugar or the reverse, and of destroying 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 proteid 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 

 doubt, therefore, of the existence of intracellular enzymes, and that 

 these substances play a conspicuous part in the metabolism of food 

 material. The lipase, the diastase, and the autolytic enzymes just 

 referred to all belong to the group that cause hydrolytic cleavages, 

 that is, they induce splitting or decomposition of the material by 

 a reaction with water. The supposition has naturally been made 

 that probably the oxidations of the body are effected also by enzymes 



