INTRODUCTION 11 



incalculably more obscure than those with 

 which we have, in a measure, become familiar 

 in ordinary chemical and physical researches, 

 nevertheless they are similarly influenced by 

 physical conditions, and they obey the same 

 chemical laws. The chief differences between 

 the reactions in the living body and those 

 which occur outside it seem to lie mainly in 

 the greater complexity of the substances con- 

 cerned, as well as in the necessity for accurate 

 adjustment of the reacting substances towards 

 each other in ways which we can at present 

 but feebly imitate. An important feature in 

 this matter of adjustment consists in that 

 state of aggregation which we call colloidal, 

 which is so characteristic of the framework 

 of living things, and by virtue of which 

 the physical conditions for many chemical 

 reactions are provided. 



A simple example perhaps may serve to 

 make the point clearer. A piece of platinum 

 wire will not bring about the ignition of a 

 mixture of coal gas and air, but if the plati- 

 num be finely divided, e. g. in the form known 

 as " platinum black " or spongy platinum, it 

 will do so. If the platinum be still further 

 divided, it assumes the condition known as 

 " colloidal platinum," and it is then capable 

 of promoting many other chemical changes in 

 a manner closely resembling, and perhaps 

 essentially similar to, that characteristic of 

 many organic ferments. 



Of course it is not meant to suggest that the 



