Some Physical Properties of Protoplasvi 253 



dicular to that of another to which it is attached. On stretching, 

 the axes of the molecules are pulled into line with each other. 

 Elongation is thus doubled. As one spiral coil will permit an exten- 

 sion of 300 per cent, a stretch of 600 per cent is thus obtained. 

 This surpasses the usual 400 per cent and approaches the possible 

 maximum of 800 per cent for rubber. 



The source of energy was also given consideration.^'' The residual 

 valences of double bonds are insufficient because in stretched rubber 

 they are spaced too far apart. Mack, therefore, assumed that the 

 source of attraction lies in van der Waals' forces between hydrogen 

 atoms attached to carbon atoms. 



Contraction results, says Meyer^^, because the extended state of 

 a long chain molecule is thermodynamically a less probable one 

 than the contracted state. The extended form has only a single 

 geometrical possibility, whereas the contracted form has many. The 

 extended chain will thus have a tendency to contract, and this 

 appears to be true not only for rubber, but for all elastic synthetic 

 polymers, for muscle, and for protoplasm. Thus we see that deduc- 

 tions made from considerations of rubber apply to living matter. 



Proteins are the substances, and their folded chains the molecular 

 forms probably responsible for the elasticity of protoplasm. This is 

 the consensus of opinion, but it has had its opponents. Controversy 

 over the form of polypeptide molecules entered early into the stereo- 

 chemistry of proteins. Solid spheres, hollow spheres, chains, fibers, 

 coils, nets, and lattices have all had their advocates. By the time 

 most chemists had agreed on the polypeptide chain for proteins, with 

 side-chain linkages establishing two and three dimensional lattices, 

 there arose renewed support of the hollow sphere, based primarily 

 on mathematical analysis. ^^ 



The chief objection to a hollow sphere is the difficulty of doing 

 anything with it structurally. If the 32,000 molecular weight protein 

 is a complete and closed hollow sphere in itself, it would be difficult 

 to construct 64,000, 96,000, etc., molecules from it, as Svedberg sug- 

 gests is done in nature. Mechanical properties, such as elasticity, 

 tensile strength, and the extraordinarily high water holding capacity 

 of jellies would be equally difficult of interpretation. To attempt to 

 satisfy the physical properties of protoplasm with a spherical mole- 

 cule is rather like asking a weaver of cloth to make his fabric of 

 sand instead of threads. 



^Science, 85. 76. 1937. 



