ACTION OF ENZYMES 47 



of reacting with another molecule, which also may require similar 

 changes in its molecular constitution before it is fitted to react ; 

 and (2) the physical forms of energy which act between the dissolved 

 molecule and its solvent, such as the velocity of movement of 

 the molecule through the solvent, and, at any rate in the case 

 of the colloidal molecule, probably surface tension at the surface 

 between the dissolved molecule and its solvent. 



Action between the dissolved molecule and its solvent, which 

 must also come in as a factor in preparing for chemical reaction, 

 or altering the resistance to chemical reaction, is seen in the different 

 ionising powers of different solvents for salts, and in the different 

 degrees of association of different dissolved substances in different 

 solvents. For example, the ionisation of inorganic salts in water 

 as compared to organic solvents, and the duplicate and higher 

 molecular weights of organic substances in an associating solvent, 

 such as benzol, compared with another solvent, such as alcohol. 

 As proof of this connection, it may be pointed out that the more 

 ionised a dissolved substance is the more quickly it reacts, showing 

 that the molecular resistance to reaction has been broken down ; 

 and the very different velocities of reaction of the same substances 

 in different organic solvents (see p. 132) must be due to corre- 

 sponding differences in molecular resistance to reaction in these 

 different media. 



The first of these factors is that which will probably be most 

 effective in entirely stopping a reaction, and the latter that which 

 is effective in rendering reactions in solution as a general rule 

 much slower than those which occur in gaseous mixtures. 



It is by modifying the action of these opposing forms of 

 energy, in some way, 1 that the catalyst or enzyme or living cell 



1 The mode of action is at present unknown to us, the hypotheses thereon 

 will be given later (see p. 126) ; the important fact to realise here, apart from any 

 hypothesis, is that the catalyst acts as an energy conductor or transformer for 

 chemical energy, and varies the amount of energy necessary to be transformed 

 in various other directions before the reaction can ensue, it makes the path easy 

 between two forms of energy. Further, it may be pointed out that the modus 

 operandi of energy -transformers lies always without the pale of our knowledge 

 in the case of other forms of energy, just as much as in the case of chemical 

 energy, where the matter has given rise to so much thought and discussion. We 

 do not really know, for example, the mode in which an electric current heats a 

 wire, or how an electric current magnetises iron, and no other substances ; all 

 we have is hypothesis, just as we have for how a catalyst produces its trans- 

 formations of chemical energy. 



