CHAPTER I 



PHYSICAL CHEMISTRY IN ITS RELATIONS TO 

 PHYSIOLOGICAL CHEMISTRY 



Importance. Among the most striking advances in physio- 

 logical chemistry in recent years are those in which the methods 

 and principles of physical chemistry have been brought to the 

 aid of biochemists. Investigation of the properties of solutions, 

 of dissociation, osmotic pressure, surface tension, of colloidal 

 solutions, adsorption, diffusion, mass action, ionic equilibrium, 

 hydrogen-ion concentration and many other fields have direct 

 bearing on problems connected with the functioning of the cells 

 and tissues. In fact the continuance of cell activity is insep- 

 arably bound up with physicochemical phenomena, absorption, 

 secretion, excretion, growth, muscular contraction and an end- 

 less list of other functions of living matter are carried out in 

 conformity with physicochemical laws. The importance of 

 physical chemistry in biochemical work is thus apparent. It is 

 not within the scope of this book to enter into extended dis- 

 cussion of physicochemical fields. However, some of the more 

 important phases of the subject will be presented briefly. 



Osmotic Pressure. It is a well-known fact that a gas exerts 

 a definite pressure, and that this pressure is inversely propor- 

 tional to the volume. If the volume is halved, the pressure is 

 doubled, etc. The volume of a gas allowed to expand increases 

 %73 of its volume at 0C. for a rise of 1C. Also if an amount 

 of a gas equal in grams to the figure expressing its molecular 

 weight is contained in a 22.4 liter container, it will exert 1 

 atmosphere pressure. These facts are expressed as the funda- 

 mental gas laws. 



It has been discovered that dissolved substances also exert a 

 pressure which in many respects behaves in accordance with 



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