Viscosity Changes of Protoplasm 169 



sary factor in the streaming of the plasmasol. If the ameba is to 

 be considered as a contractile sac filled with fluid, one would 

 expect that the movement of the fluid would always be accompanied 

 by an inward displacement of the contractile wall. This, however, 

 is not always the case. Specifically, in an ameba capped with an 

 oil drop, a steady fountain streaming is maintained for hours despite 

 the fact that no change occurs in the oval contour of the cell. In 

 this instance it is evident that the constriction of the plasmagel 

 wall is not essential for active streaming . . . An alternative sug- 

 gestion as regards the cause of streaming would be that the volume 

 changes inherent in the sol-gel transformations may generate the 

 flow." Their objection to Mast's view is based on the observation 

 that "a steady fountain streaming is maintained for hours despite 

 the fact that no change occurs in the oval contour of the cell." I 

 wonder if they observed what went on inside of the ameba as 

 carefully as Mast (1926) did. He occasionally noted monopodal 

 amebae that were unattached except at the tip of the posterior end, 

 so that locomotion was prevented, (p. 400) , "In such specimens 

 the movements of the plasmasol and the plasmagel are precisely the 

 same as they are in moving specimens, but in reference to points 

 in space, the plasmagel actively moves backward instead of being 

 at rest. This gives the appearance of typical fountain streaming." 

 (p. 401), "This seems to indicate that in these specimens the plas- 

 masol flowed through the elongated canal in the plasmagel, that 

 when it reached the anterior end it spread out in all directions, 

 deflected backward, came in contact with the anterior border of the 

 plasmagel tube and gelated here, extending this tube which moved 

 backward as rapidly as it was built up, sliding under the plasma- 

 lemma which everywhere remained stationary." Mast does not 

 explain further, so I venture to extend the explanation a little. 

 Continuous contraction of the posterior end of the gel layer pulls 

 the plasmagel wall backward. This posterior end is also continually 

 solating and thus keeping a balance between sol and gel. It 

 would be rather difficult to explain this backward pull on the basis 

 that the contractile tension of the gel layer was due to an elastic 

 recoil from stretching. Such a sessile ameba might very well con- 

 tinue fountain streaming without much if any distortion of the 

 posterior end such as Marsland and Brown record. Their suggestion 

 that "the cause of the streaming would be that the volume changes 

 inherent in the sol-gel transformations may generate the flow" 

 seems to me unwarranted, because the same factors are involved in 



