Proteins and Protoplasmic StriLcture 33 



in internal energy. If, however, the chains become oriented enough 

 to produce crystalHzation, the internal energy decreases, due to the 

 liberation of heat of crystallization (21, 37). In a normal elastic 

 solid, such as a steel spring, stretching results in an increase in the 

 internal energy by pulling the atoms out of their troughs of minimal 

 potential energy. Thus, while rubber becomes warmer on being 

 stretched, metals become cooler. This fundamental difference 

 enables one to detect rod-shaped molecules. It has been established 

 with the polarizing microscope and the X-ray that muscle owes its 

 physiological properties to the elongated protein molecules of myosin 

 (3, 37) . It is especially interesting, therefore, that muscle fibers on 

 contracting have been found to exhibit a thermal behavior com- 

 pletely similar to rubber (23). The contraction of muscle is thus 

 due to a coiling up of its myosin molecules. 



Spinning Capacity. It is well known that many proteins possess 

 the capacity to be spun out into thin strands after denaturation. For 

 instance, Meyer and Jeannerat (22) have found that long threads 

 could be spun out from the viscous, liquid contents of the silk gland 

 of the silkworm. Although the contents of the gland were soluble at 

 pH 10, the threads were not. This indicates that they were denatured 

 in the spinning. Such threads were reversibly extensible on stretch- 

 ing, but if held on a stretch for 10-30 seconds, crystallization of the 

 micells took place and the elasticity disappeared. The stretched 

 threads yielded a crystalline X-ray pattern, but the liquid silk was 

 amorphous until it was dried. Seed globulins can be denatured in 

 urea solutions and can then be spun out into elastic fibers (3) . On 

 stretching, the fibers crystallize in the fully extended form. It is 

 interesting that these long chains were produced from corpuscular 

 proteins. 



Many workers have observed that plasmolysis may produce very 

 long strands of protoplasm extending between the protoplast and the 

 cell wall (cf. 13) . After touching a plasmolyzed protoplast of onion 

 with a microdissection needle, Seifriz and Plowe (45) drew out 

 long, thin strands which were, in some cases, so fine as to be invisible, 

 except for globules along their lengths. When the tension was 

 released, the strands slowly contracted. It appears, therefore, as if 

 the surface of a protoplast, at least, can be spun out like some pro- 

 teins. Scarth (40) has likewise pointed out that strands of streaming 

 protoplasm, when stretched by osmotic swelling, snapped and 

 crumpled up like a solid thread, and then reverted to a fluid con- 

 dition. 



