INTRODUCTION 11 
inealeulably 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 
s ** 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 
