THE PHYSICAL CHEMISTRY OF PROTOPLASM 239 



tion of protoplasm were all based upon its color reactions to various 

 staining agents. These sometimes led to erroneous conclusions, 

 because of the effects of the staining agent itself upon the tissue; 

 some stains are poisonous and result in the death of the protoplasm, 

 others do not easily penetrate the semi-permeable colloidal mass, 

 others are themselves changed by the oxidizing or reducing action 

 of the protoplasm, etc. Again, colloidal adsorption effects often 

 lead to the so-called " capillary segregation " of added staining 

 materials. So that this method of study must be used with great 

 care, or wholly erroneous conclusions will be reached, and many of 

 the earlier reports have subsequently been found to be incorrect. 



The recent improvements in the apparatus and methods for 

 the determination of hydrogen-ion concentration have afforded a 

 much more trustworthy method of determining the actual acidity 

 or alkalinity of such materials than is obtained by color reactions, 

 and this method is now being extensively used in the study of the 

 reaction of active protoplasm. 



It must be kept in mind that protoplasm is an heterogeneous 

 mass and not an homogeneous solution, so that it is not always 

 possible to determine the actual conditions as to neutrality of dif- 

 ferent parts of the protoplasm of a single cell, for example. Hence, 

 one of the best methods of determining the reaction which is favor- 

 able to the life and activity of any given type of protoplasm is to 

 investigate the reaction of a liquid medium in which the cells 

 live and grow; this plan being based upon the assumption that a 

 cell is not likely to have a reaction different from that of the 

 medium which is favorable to its growth. 



The results of all of the many investigations which have 

 dealt with this problem point to the conclusion that the normal 

 reaction for living protoplasm is either neutral or very faintly 

 alkaline; but that it becomes acid when the cell is working in the 

 absence of sufficient oxygen, and after the death of the cell. 



The first effect of a change in the reaction toward acidity of the 

 protoplasm is a decrease in the rate of respiration of the tissue, 

 while increased alkalinity stimulates respiratory activity. When 

 carried to the point of actual acidity, the respiratory coefficient 

 becomes negative, and the cell actually gives off carbon dioxide 

 because of the stoppage of the synthetic processes. 



A second effect of change in reaction of protoplasm is to alter 

 the enzymic activity of the cell. As has been pointed out, enzymes 



