Introduction 9 



bond, namely, its probable function in the hydration of proteins. 

 Water of hydration is not our present interest, though an important 

 subject in biology. Reference is made to it in order to show further 

 application of the hydrogen bond. 



The hydrogen bond will probably serve the biologist well in his 

 studies on the mechanism of protoplasmic behavior. But the physical 

 chemist promises still more for the future. Pauling'" calls attention 

 to resonance as a likely factor in the physiological activities of living 

 matter. Resonance describes the state of a molecule when one of 

 several alternate structures are possible, and the actual normal state 

 of the molecule is not represented by any one, but by a combination 

 of them. The molecule is then said to resonate among the several 

 possible electronic or valence-bond structures. 



Little has as yet been done with resonance in the interpretation 

 of vital processes. The future of it in biology cannot, therefore, be 

 predicted with certainty, but it opens up a great field of possibilities. 



The biologist is confronted with many qualities of living matter 

 which will remain pure physiological problems for some time to 

 come, but the list of properties which are now fully or partially 

 capable of pure physical or chemical analysis is a long one; it includes 

 elasticity, tensile strength, contractility, thixotropy, gelation, fluidity, 

 non-Newtonian behavior, streaming, amoeboid movement, structural 

 continuity, birefringence, symmetry, asymmetry, spirality, liquid 

 crystallinity, and selectivity. 



It is truly an encouraging sign in the progress of science when 

 properties of protoplasm such as contractility and structural organi- 

 zation, which heretofore were so little understood, can now be inter- 

 preted in terms of folded polypeptide fibers, interlocking side chains, ^ 

 hydrogen bonds, and asymmetry of the carbon atom. I 



