26 The Structure of Protoplasm 



possible configurations of the molecule and, hence, will occur very 

 infrequently under these conditions (18, 21). Stretching the system 

 can be made to produce extension and alignment of the flexible 

 chains with a lessening of the probability of the system and a con- 

 comitant decrease in the entropy. Double refraction first appears on 

 deformation. When the stress is released, thermal agitation of the 

 different parts of the chain tends to produce more random configura- 

 tions and a more probable state. Contraction results as the chains 

 coil up. Likewise, in a system of inflexible rods, a random arrange- 

 ment is most probable. In either case, cooling would tend to produce 

 a more oriented, and warming, a more disoriented state. It is there- 

 fore especially interesting that Ullrich (47) has succeeded in pro- 

 ducing double refraction in the cytoplasm of the epidermal cells of 

 the bulb scale leaves of onion by cooling the tissue to 2°C. On 

 warming the tissue to 3° or 4°C., the effect disappeared. He reports 

 that death of the cells produced a sudden isotropy, so that it is 

 doubtful if the double refraction can be ascribed to injury. 



With the exception of the cell membranes, the continuous phase 

 of protoplasm is aqueous. Several investigators (17, 38) have found 

 that water injected into cytoplasm is taken up by it without vacuole 

 formation. In many cases, it is probable that the high concentration 

 of water in protoplasm and the resultant hydration of the micells 

 interferes with double refraction phenomena. Rinne (39) has 

 emphasized that the high dielectric constant of water tends to pro- 

 duce a weakening of the electrochemical fields of force between 

 micells and reduce birefringence. In support of this, he has pointed 

 out that the double refraction of the myelin sheath of nerve decreases 

 as the water content increases, even though it is evident that the 

 orientation of its micells persists, as indicated by the retention of its 

 form. Ullrich (47) has also found that a reduction in the water con- 

 tent of protoplasm, brought about by plasmolysis with hypertonic 

 salt or sugar solutions, produced birefringence in onion cell cyto- 

 plasm. 



ADDITIONAL EVIDENCE FOR ROD-SHAPED BODIES 



The observations made with the polarizing microscope indicate 

 clearly that submicroscopic rods of some sort are present in cyto- 

 plasm, but they do not tell what the rods are or if any actual 

 structure is conferred on the protoplasm by their presence. Fortu- 

 nately, other experimental methods have been employed. 



For instance, Moore (28) has found that the coenocytic plas- 



