12 PHYSICAL CHEMISTRY 



if it is insoluble in the second phase it remains concentrated in 

 the phase boundary, and is said to be adsorbed by the second 

 phase. 



Electric polarization, such as was described above in regard 

 to nerve and muscle, decreases the surface tension. Hence 

 stimulation is followed by local increase in surface tension. 

 Surface tension changes cause ameboid movements and cell 

 division. Some suppose that muscular contraction is due to 

 surface tension changes, but if this is the case the surfaces con- 

 cerned must be those of colloidal particles or internal structures, 

 as the surface of the muscle fiber is not large enough to account 

 for the force of contraction. 



We thus see that a knowledge of what is ordinarily called 

 chemistry is not sufficient for the biochemist dealing with med- 

 ical or biological problems. Beside the reactions between pro- 

 teins, carbohydrates, fats, and many organic and inorganic 

 compounds as usually considered by the biochemist, we are 

 concerned with such physico-chemical processes as the rate of 

 reaction and the position of equilibrium as expressed in the law 

 of mass action, with the effect of ions, especially H* and OH', 

 osmotic pressure, phase boundaries and the surface tension, dif- 

 fusion, adsorption and electrical polarization phenomena that 

 occur at the phase boundaries, with colloids and their aggrega- 

 tion states, whether gels or sols, with the effect of salts on these 

 colloids, and especially on the plasma membrane which is ap- 

 parently a colloidal structure, with the enzymes and their colloidal 

 state and dissociation, and finally with certain reactions that are 

 apparently accelerated by cell structure, presumably through the 

 intermediation of adsorption phenomena. 



Definitions of Physical Properties of Aqueous Solutions 



There is a group of properties of water which are affected pro- 

 portionately by the introduction of a solute. These are called 

 by Washburn, 1915, the colligative properties of the solution. 

 If the solution is sufficiently dilute, the effect of the solute on 

 its colligative properties is independent of the chemical nature 

 of the solute, and determined solely by the number of dissolved 

 particles (molecules -(- ions). The colligative properties are: 



1 — Vapor Pressure. If water is introduced into a vacuum 



