260 PROTOPLASM 



characteristics necessary for molecular orientation. The mole- 

 cule has a positive and a negative charge; the former is on the 

 two hydrogen atoms, and the latter on the oxygen atom. At a 

 distance, such a molecule is electrically neutral; but viewed 

 nearby, it is positive or negative depending on the position. 

 The negative oxygen atom of one water molecule would attract 

 and hold the two positive hydrogen atoms of another water 

 molecule close by and with a force which may equal its hold on 

 its own two hydrogen atoms. We may regard the valence 

 bonds within a water molecule as chemical and those between 

 adjoining molecules as physical, but it amounts to essentially 

 the same thing in the end, for the hydrogen atoms and the oxygen 



Q 







CI b c d e 



Fig. 138. — Diagrams illustrating the polarity of water. 



atoms exert forces on the surrounding molecules which are no 

 less chemical in nature than those holding the atoms within the 

 molecule together. Fluidity depends upon the tautomeric 

 shifts that take place between one water molecule and another. 

 (As water is slightly ionized, the hydrogen nuclei are able to 

 shift to some extent from one water molecule to another, but 

 fluidity does not necessarily depend upon this.) Bragg states 

 that water molecules are always in partnership but always 

 changing partners. Even liquids in solution yield diffraction 

 patterns indicative of some kind of arrangement. We thus see 

 how polarity leads to orientation and it in turn to continuity 

 in structure in a liquid system and in so simple a one as water. 



The possibilities in proteins are infinitely greater. A theory 

 of the structure of elastic gels, wherein the gel framework is 

 assumed to be a loosely joined, semirigid, elastic framework built 

 of long, slender, and crystalline fibers, satisfies not only the 

 known properties of jellies but also those of protoplasm, as far 

 as our present knowledge goes. Such a theory makes particularly 

 clear how it is that protoplasm can exhibit properties so typical 



