144 The Structure of Protoplasm 



tiie present experiments it was found necessary to use a force of 

 16,500 X gravity to secure an adequately rapid displacement of the 

 pigment granules through the firmly set plasmagel. But even this 

 force is not sufficient to dislodge the granules except under the 

 liquefying action of pressures greater than 1,500 Ibs./in.- At 

 atmospheric pressure, a force of 18,680 X gravity, the highest 

 immediately available at the Naples laboratory, gave practically no 

 pigment displacement even with prolonged centrifugation. 



The centrifugal force used in the experiments was 16,500 X 

 gravity, and each sample of eggs, compressed to the desired degree, 

 was centrifuged for a period just sufficient to displace the cortical 

 pigment into a compact zone at the centrifugal pole of the cell. In 

 each case the eggs of a single female were fertilized and allowed to 

 develop in the usual fashion until the first furrows began to appear. 

 Then, without delay, the control and experimental samples were 

 placed in their respective sections of the centrifuge-pressure bomb, 

 and the desired pressure was established in the pressure section. 

 The operations were so fixed that, at the time when the pressure 

 was applied and the centrifuging begun, about 50 per cent of the 

 eggs possessed furrows of greater or lesser depth. 



The very marked solating action of the higher pressures upon 

 the pigment-laden cortical protoplasm of the cleaving egg is clearly 

 shown in Figure 7. All of these eggs were centrifuged at the same 

 time for 2V2 minutes. It may be noted that each of the pressure- 

 treated specimens displays, in addition to the usual oil, hyaline, and 

 yolk zones, a sharp pigment zone, at the centrifugal pole. This zone is 

 absent in the atmospheric specimens.-"' Also it may be noted that the 

 one egg which had just completed the first cleavage by the time the 

 suppressing action of the pressure could take effect displays the 

 same physical properties as the others. 



Assuming that the firmness (gelation percentage) of the cortical 

 gel is in proportion to the minimum centrifuge time required to pro- 

 duce a standard zoning of the pigment granules, in the range of 

 pressure wherein an effective displacement occurs, it is possible to 

 plot the gelation values as a function of pressure. These data (Fig. 2) 

 indicate, not only that the very firm plasmagel of the cleavage period 

 shows the same relative susceptibility to the solating effects of 

 pressure as other cellular gels, but also that the inhibition of furrow- 

 ing is quantitatively related to the concomitant shifts in the sol ^ gel 

 equilibrium. 



