The Mechanism of Chemical Change in Living Organisms 639 



WEEKLY EVENING MEETING, 



Friday, March 24, 1916. 



Sir James Reid, Bart., G.C.Y.O. K.C.B. M.D. LL.D. F.R.C.P., 

 Vice-President, in the Chair. 



Professor W. M. Bayliss, M.A. D.Sc. F.R.S. 



The IVIechanism of Chemical Change in Living Organisms. 



If we take a general view over the large field of chemical reactions 

 known, we notice that there is a great variety in the rate at which 

 these reactions take place. Some, and especially those in which 

 electrical forces play a part, reactions between inorganic ions, are 

 practically instantaneous. They are familiar to all in the precipita- 

 tions of the analytical chemist. Others, such as the hydrolysis of 

 cane-sugar by water, are so slow as to be incapable of detection at 

 ordinary temperatures, unless a very long time is allowed. There 

 are, moreover, all possible stages intermediate between these extremes. 

 Reactions between carbon compounds are, generally speaking, com- 

 paratively slow ; but, as the name " organic " indicates, they are the 

 characteristic changes of the living cell. 



Early workers in the domain of physiological chemistry — 

 Schonbein, for example — were struck by the fact that reactions which 

 require, in the laboratory, powerful reagents, such as strong acids and 

 high temperatures, to make them take place at a reasonable rate, 

 occur rapidly in the living organism at moderate temperatures and in 

 the presence of extremely weak acids or alkahs. I may refer to the 

 decomposition of proteins into their constituent amino-acids, which 

 is a part of the normal process of digestion, but, when ordinary 

 laboratory methods are used, requires boiling for several hours with 

 concentrated hydrochloric or sulphuric acid. 



The problem before us, then, is to discover how a slow reaction 

 can be made to go faster. The most obvious and well-known method 

 of doing this is by raising the temperature ; but this is clearly out of 

 the question in living cells. Another possibility is to make use of 

 mass action, increasing by some means the effective concentration of 

 the reacting substances ; in this way the number of contacts per unit 

 time would be raised. This is possible in the cell. There remains 

 a third, the formation of an intermediate compound with another 

 substance. This compound may be supposed to be both formed and 

 again decomposed at a rapid rate, so that the total time taken is 

 much less than that of the original reaction. 



