PHYSIOLOGICAL GRADIENTS 91 



some to constitute a formidable difficulty for this con- 

 ception, but I believe the difficulty is only apparent. It 

 is of course true that differences in the velocity alone of 

 a pure chemical reaction do not give rise to qualitatively 

 different products of reaction. In protoplasm, however, 

 we are concerned, not with a pure chemical reaction, 

 but with an exceedingly complex system, involving both 

 physical and chemical factors. The coefficients of 

 quantitative alteration of the different factors of the 

 protoplasmic system in relation to quantitative external 

 factors, such, for example, as temperature, are of very 

 different magnitudes. The temperature coefficients of 

 most chemical reactions differ widely in magnitude from 

 those of many physical processes, and there is even 

 considerable difference in the temperature coefficients 

 of different chemical reactions. A change in tempera- 

 ture then does not alter the different component factors 

 of the protoplasmic system to the same degree, but alters 

 some much more than others. Consequently such a 

 change, which is nonspecific and quantitative for each 

 factor, may alter the system as a whole in such a way 

 that chemical reactions which could not take place 

 before the change may occur after it, and vice versa. 

 Changes in concentration of reacting substances do in 

 many cases determine different products of reaction, 

 and change in temperature may bring about changes 

 in concentration of substances in protoplasm in various 

 ways, e.g., by alteration in the water content, the dis- 

 persion of the colloids, adsorption, and by change in the 

 rate of chemical reaction itself, which may change the 

 concentration of the products of a given reaction and so 

 determine a second reaction which could not take place 



