322 PROTOPLASM 



It is difficult to correct for the temperature effect on pH, as 

 the coefficient is apparently quite variable, although the change 

 in blood measurements due to it is now fairly well established. 

 Measurements of the pH of blood should be made at 38°C. If 

 made at a lower (room) temperature, the pH changes 0.01 for 

 every degree, which means that with lower temperature blood 

 becomes more alkaline. Normal blood has a pH of 7.35 to 7.43 

 at 38°C., with 7.38 the usual value. At 20°C., it will be about 

 7.55. 



The lipoid error can at times be very great and is not easily 

 corrected. Also not readily allowed for are the color errors in col- 

 loidal systems. Deutsch has shown that pH indicators do not 

 give the correct colors in systems with great adsorptive surfaces 

 such as colloidal solutions, gels, and the like. There is a dis- 

 placement of the pH equilibrium and adsorption of the dye, 

 resulting in colors from those quite different in homogeneous 

 solutions. (This is probably true only of those dyes the undis- 

 sociated form of which is lipoid soluble and not of amphoteric 

 dyes.) 



The Role of Hydrogen Ions in Life. — The part that hydrogen 

 ions play in vital processes is one of the outstanding biological 

 problems of today. Perhaps we have deified the hydrogen ion, 

 but there is every reason to believe that while later work may 

 take away from hydrogen some of the significance that we are 

 now attaching to it, it will always remain one of the most impor- 

 tant ions in physiological reactions. Aside from its acid proper- 

 ties, its minimum size and maximum speed place it in a unique 

 position among ions. 



The role of hydrogen in life is so great and so widespread that 

 one can hardly mention a process of an organic nature that is not 

 influenced by these ions. Their effect in the nonliving world is 

 probably no less extensive. Leather tanning, breadmaking, 

 brewing, aging of wines, tea curing, fermentation reactions, 

 electroplating, chemical precipitations, the settling of muddy 

 water, and the productiveness of soil are all properties the rate 

 and success of which depend upon pH. 



Soil problems play an important role in agriculture and in 

 natural plant distribution. They involve the influence of acidity 

 on soil reactions, plant reactions, and the relationship between 

 plant and soil, such as the availability of soil nutrients to the 



