158 The Structure of Protoplasm 



"Reorganization of a fluid cylinder into drops will occur when the length 

 exceeds pi times the diameter, provided the viscous (or plastic) resistance of 

 the material is not too great. 



'- This assumption seems fully justified from measurements on a variety of 

 cells. Each pressure increment induces the same percentage degree of solation 

 regardless of the absolute initial rigidity of the particular gel. 



^'These values frequently have been referred to as the relative viscosity of 

 the protoplasm. This term, however, fails to distinguish between measurements 

 dealing with solated, and those made upon gelated parts of the system. Further- 

 more, in a truly viscous system some displacement of suspended granules occurs 

 even under very low centrifugal forces, which is not the case in the present 

 measurements. 



''At constant centrifugal force, namely 7,000 X gravity. 



''The elongation of the pseudopodia which occurs at pressures below 2,000 

 lbs. is probably related to the observation that in this range no plasmagel- sheet 

 (Mast, '26) is present at the pseudopodial tips. Apparently this part of the 

 plasmagel system, which tends to restrain the outflow of the plasmasol, and 

 which constitutes a gelation focus when retraction is to begin, is more labile 

 than the other parts. 



'"Recently, Pease ('40) describes an acceleration of streaming in the Plasmo- 

 dium of the slime mold (Physarum polycephalum) at pressures between 1,000 

 and 3,000 Ibs./in.' This would constitute an exception to the general rule that 

 protoplasmic streaming is progressively inhibited by pressure in the physiologi- 

 cal range. Perhaps the discrepancy may be explained on the basis that in 

 Physarum the whole Plasmodium suffers reorganization in the range. The 

 acceleration may indicate that, as the contours of the protoplasmic mass are 

 changing, surface forces become active to augment the flow. This interpretation 

 is favored by the observation that the accelerated flow occurs chiefly in Plas- 

 modia which are not attached to the substratum but which are freely suspended 

 in the medium. A further factor in the acceleration may be found in the 

 reorganization which occurs in the channel walls. Thus the flow in a particular 

 channel might be augmented as a result of an anastomosis from a neighboring 

 channel. To obtain quantitative data in this connection, perhaps the technique 

 of Kamiya ('40) could be used. 



"As for example, when streaming is about to stop, or when it is barely 

 beginning. At such times the channels and the direction of flow may be highly 

 irregular. 



''At constant centrifugal force. In the case of Elodea this was 810 X gravity. 

 '"Recent work by Pease (personal communication) indicated that sol^gel 

 reactions may also be important in the migration of the chromosomes during 

 anaphase. 



"' The use of the terms plasmagel and plasmasol with reference to the cyto- 

 plasm of egg cells was first proposed by Marsland ('39a) . 



^' It is possible that the plasmagel system of the egg cell also includes some 

 of the medullary cytoplasm such as parts of the spindle and asters. 



" This observation is recorded in one of Dr. Chambers' cinema films. See also 

 Chambers ('38). 



-" The eggs of Arhacia punctulata were used in the study of the visible effects 

 of pressure upon cleavage, whereas those of Arbacia pustidosa served for the 

 measurements of the solation effects. 



-* In from 1-10 minutes, depending upon the depth to which the furrow has 

 gone, and upon the intensity (above 7,000 lbs.) of the pressure. 



''Apparently the internal conditions which result in cleavage persist for a 

 hmited time (about 15 minutes at 22° C). If the experimental inhibition is 

 prolonged beyond this, the tendency to cleave lies dormant until control eggs 

 have just begun the second cleavage. Now the eggs in which the "first" cleavage 

 has been suppressed, also begin to cleave, usually into four blastomeres directly, 



