402 RALPH S. LILLIE 



nal resistance returns. A similar reversible decline of resistance 

 takes place at the second and third cleavage, and is probably 

 general for mitotic cell-division. 



2. The minimum of resistance is found during the formation 

 of the furrow. Both the decline and the return of resistance 

 are rapid, the greater part of each phase occupying four to five 

 minutes (at 22°). Some increase of susceptibility is apparent 

 ten or twelve minutes before the first appearance of the furrow. 



3. A decrease in the coherence or extensibility of the plasma- 

 membrane at the time of cytoplasmic di\dsion is thus indicated. 

 The earlier observations of Lyon and other investigators have 

 shown that an increase of susceptibility to poisons, heat, and 

 other injurious conditions, together with an increased output 

 of CO2, takes place at this time, i.e., simultaneously with this 

 change in the membrane. The above facts constitute additional 

 evidence that an intimate connection exists between the general 

 physiological condition of the egg and the physical state of the 

 plasma-membrane . 



4. The above change in the membrane is probably associated 

 with an increased permeability to water-soluble substances 

 and a decreased electrical polarization; this latter change, ac- 

 cording to the law of electrocapillarity, involves increased sur- 

 face-tension. From the analogy with the general stimulation- 

 process, it seems also probable that the change of polarization 

 acts upon the conditions within the dividing cell (oxidations, 

 etc.) in a manner analogous to the similar change in electrical 

 stimulation in general. 



5. The following hypothesis of cytoplasmic division is put 

 forward. The change of form is the result of two chief factors: 



(1) a definitely localized increase of surface-tension, resulting 

 directly from increased permeability and decreased electrical 

 polarization of the cell-surface, over two symmetrical areas 

 centering at the poles and extending to near the equator; and 



(2) a secondary or adjuvant effect of the same kind due to the 

 diffusion of electrolytes (e.g., acid derived from oxidations) 

 from the astral centers or centrioles, which become chemically 

 active at this time. These centers appear to represent aggre- 

 gations of a special colloidal material which undergoes oxidation 

 when the cell-surface undergoes depolarization. 



