LAWS OF SOLUTION 3 



is more than this ; it is a laboratory furnished not only with the equip- 

 ment of the chemist but directed in the harmonious operation of its 

 many activities by a guiding hand which far surpasses anything else known 

 to man. Chemical transformations that require for their accomplishment 

 the greatest skill proceed without apparent difficulty in the cell. To 

 what are these changes due? What is the nature of the chemical rea- 

 gents and forces, and what is the directive influence that guides them 

 in their varied activities? To these, which are among the great ques- 

 tions of general physiology, the reply may be given that the reagents 

 are the ferments or enzymes, and that the directive influence operates 

 through the susceptibility of enzymic activities to changes in the envi- 

 ronment in which the enzymes are acting. In many cases these changes 

 can be explained on a physicochemical basis as dependent upon the 

 known laws of mass action or surface tension; in other cases they de- 

 pend on purely chemical changes in the cell contents, such as changes 

 in reaction or the accumulation of chemical substances that act like 

 poisons on the enzyme. But there are still others that appear to depend 

 on influences which as yet are quite unknown to the physical chemist, 

 such as the changes in cell activity that can be brought about by the 

 nerve impulse. 



These preliminary remarks will serve to indicate the problems with 

 which we must first occupy our attention. They concern the physico- 

 chemical nature of saline solutions and of colloids, and the general na- 

 ture of enzyme action. The knowledge which we acquire will be found 

 to be of value, not only because it will help us to understand the nature 

 of the workings of the normal healthy cell, but because, here and there, 

 it will indicate possible causes for derangement in cellular function and 

 suggest rational means by which we may attempt to rectify the fault. 



THE PHYSICOCHEMICAL LAWS OF SOLUTION 



The Gas Laws 



Three fundamental principles of general chemistry serve as the basis 

 for an understanding of the nature of solutions. The first is that if 

 we take a quantity of any gas equal to its molecular weight in grams 

 (called a gram-molecule or for sake of brevity a mol), it will occupy ex- 

 actly 22.4 liters at a temperature of C. and a pressure of 760 mm. Hg. ; 

 the second is that, as we compress a gas, its pressure will increase in exactly 

 the same proportion as the volume diminishes (the volume of a gas is in- 

 versely proportional to its pressure) ; the third is that all gases expand by 



