THE PRESIDENTIAL ADDRESS 7 
to feel that my brief summary of the facts will make you realise how 
much more definite, how much more truly chemical, is our present 
knowledge than that available when Michael Foster wrote. Ability 
to recognise the progress of such definite ordered chemical reactions 
in relation to various aspects of living activity characterises the 
current position in biochemistry. I have chosen the case of muscle, 
and it must serve as my only example, but many such related and 
ordered reactions have been studied in other cells and tissues, from 
bacteria to the brain. Some prove general, some more special. 
Although we are far indeed from possessing a complete picture in 
any one case we are beginning in thought to fit not a few pieces 
together. We are on a line safe for progress. 
I must perforce limit the field of my discussion, and in what 
follows my special theme will be the importance of molecular 
structure in determining the properties of living systems. I wish 
you to believe that molecules display in such systems the properties 
inherent in their structure even as they do in the laboratory of the 
organic chemist. The theme is no new one, but its development 
illustrates as well as any other, and to my own mind perhaps better 
than any other, the progress of biochemistry. Not long ago a 
prominent biologist, believing in protoplasm as an entity, wrote : 
‘But it seems certain that living protoplasm is not an ordinary 
chemical compound, and therefore can have no molecular structure 
in the chemical sense of the word.’ Such a belief was common. 
One may remark, moreover, that when the development of colloid 
chemistry first brought its indispensable aid towards an under- 
standing of the biochemical field, there was a tendency to discuss 
its bearing in terms of the less specific properties of colloid systems, 
phase-surfaces, membranes, and the like, without sufficient reference 
to the specificity which the influence of molecular structure, where- 
ever displayed, impresses on chemical relations and events. In 
emphasising its importance I shall leave no time for dealings with 
the nature of the colloid structures of cells and tissues, all important 
as they are. I shall continue to deal, though not again in detail, 
with chemical reactions as they occur within those structures. Only 
this much must be said. If the colloid structures did not display 
highly specialised molecular structure at their surface, no reactions 
would occur; for here catalysis occurs. Were it not equipped 
with catalysts every living unit would be a static system. 
With the phenomena of catalysis I will assume you have general 
acquaintance. You know that a catalyst is an agent which plays 
only a temporary part in chemical events which it nevertheless 
determines and controls. It reappears unaltered when the events 
are completed. ‘The phenomena of catalysis, though first recognised 
early in the last century, entered but little into chemical thought 
