Many substances burned in the body—sugar, for example—may undergo slow oxidation in alkaline solution in the presence of atmospheric oxygen . In the body, however, it is burned at a faster rate, leading to the conclusion that some other substance or substances are necessary. The search for such substances has led to the discovery of so called oxidizing enzymes, which oxidize many organic substances. It is characteristic of an enzyme, however, that it accelerates but one reaction. For the complete oxidation of grape sugar, for instance, it is supposed that a series of enzymes is necessary. This must remain for some time a supposition, as no pure substance or mixture of soluble substances has been extracted from the body that will completely oxidize grape sugar.
It might be concluded that "life" is essential to such oxidations, but such is not the case. In some instances ground up tissue, free from entire cells, absorbs oxygen and gives out at a rapid rate. It is evident that some substances are completely oxidized in the process. The question has been raised as to whether the cell structure which has not been completely destroyed in grinding the tissue be necessary for the oxidation. In certain experiments Harden and McLean failed to observe respiration in juice pressed out of muscles and other tissues. Warburg and Meyerhof ground nucleated red-blood corpuscles with sand, finding that the mass did not absorb oxygen or give out , whereas the original cells did. Warburg tried to destroy the structure completely by grinding corpuscles in a steel box; with steel spheres rotating at such high speed it was found necessary to cool the box with ice in order to prevent injury to the corpuscles by heat (Barnard & Hewlett apparatus). All microscopic structure was destroyed and respiration ceased.
In other experiments, Warburg ground up liver cells, passing the juice through a Berkefeld filter. The respiration of the juice was but five per cent. of that of the corresponding amount of liver cells. But when a coarser filter was used which allowed the passage of cell granules, the oxidation was found to increase to twenty per cent. of that of intact cells.
If blood corpuscles be placed in water, or in certain solutions, the hemoglobin passes out of them, they become pale and are called "ghosts." This liberation of the hemoglobin, known as "laking," is a kind of cytolysis. Warburg laked nucleated red-blood corpuscles of a goose, finding that respiration continued in the "ghosts," but did not occur in the fluid procured by laking.
Such experiments seem to show that the presence of solid structures, granules, etc., accelerates the respiration, since no substances were eliminated in the process of grinding. It is possible that the solid structures act in the same way, as does finely divided platinum (called platinum
