OF VITAL PHENOMENA 169 



is shown by their red color, and indicators swallowed by protozoa 

 have shown an acid reaction of the vacuole contents. But it is 

 impossible to determine the reaction of the protoplasm itself, 

 except t6 say that it is less acid than the isoelectric point of the 

 proteins or lipoproteins of which it is formed. As soon as the 

 lactic acid reaches the outer surface of the plasma membrane 

 it is burned, provided 2 is present. As will be shown later, the 

 oxidase concerned is probably associated with the plasma mem- 

 brane, possibly adsorbed to its outer surface. Anesthetics might 

 suppress oxidation in two ways, by preventing the permeability 

 increase, or by coating the oxidase with a layer preventing the 

 access of the oxidizable substance. 



The evidence that such a process might take place in other 

 cells is found in the fact that the oxidation of the sea urchin's 

 egg increases sevenfold when its permeability increases, and War- 

 burg (191 1 b) has shown that the oxidation of erythrocytes is 

 increased on laking by freezing and thawing (provided there is 

 not too much serum or salt solution present). Warburg gives 

 as evidence of surface action the fact that alkaline sea water 

 or pure NaCl solution increases the oxidation of unfertilized 

 sea urchin eggs sevenfold whereas they do not penetrate the proto- 

 plasm. He takes experiments of Overton as evidence that NaCl 

 does not penetrate, and as evidence that NaOH does not pene- 

 trate the fact that this concentration of NaOH does not turn 

 eggs yellow that have been stained with neutral red, whereas 

 NH 4 OH of less alkalinity does. 



Colorless substances may be oxidized by cells to colored com- 

 pounds that appear as granules in the cell interiors. This does 

 not prove that oxidation occurred in the exact spot in which the 

 granules are seen. Certain granules in cells absorb or adsorb 

 and concentrate dyes so that they may remove all of the dye from 

 their surroundings. Even though an oxidation product is said 

 to he insoluble, solubility is a relative term', and the diffusion 

 of an extremely dilute solution of a colored substance cannot be 

 detected with the microscope because this instrument does not 

 make the color appear more intense than it actually is. But it 

 does not seem reasonable that all of the oxidation takes place 

 on the cell surface. Warburg (1911 b) has shown that minute 

 quantities of NH 3 , insufficient to change the reaction of the 



