CHEMICAL ASPECTS OF LIFE HOPKINS 135 



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 fol- 

 lows my special theme will be the importance of molecular structure 

 in determining the properties of living systems. I wish you to be- 

 lieve 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, more- 

 over, that when the development of colloid chemistry first brought 

 its indispensable aid toward an understanding 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, wherever displayed, impresses on 

 chemical relations and events. In emphasizing 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 specialized molecular struc- 

 ture 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 deter- 

 mines and controls. It reappears unaltered when the events are com- 

 pleted. The phenomena of catalysis, though first recognized early 

 in the last century, entered but little into chemical thought or enter- 

 prise, till only a few years ago they were shown to have great impor- 

 tance for industry. Yet catalysis is one of the most significant 

 devices of nature, since it has endowed living systems with their 

 fundamental character as transformers of energy, and all evidence 

 suggests that it must have played an indispensable part in the living 

 universe from the earliest stages of evolution. 



