Protoplasmic Streaming — Relation to Gel Structure 147 



approximately to the same form when the experiment is repeated 

 a number of times, provided the exposure to pressures in excess of 

 5,000 lbs. does not endure beyond about 20 minutes. 



Quantitative measurements of the chromatophoral expansion as 

 a function of pressure are difficult due to the extremely irregular 

 form of the pigment cell, and at the present time only qualitative 

 data are available. The same is true of centrifuging experiments 

 which have been undertaken to determine the effects of pressure 

 upon the gel properties of these cells. Without question solation does 

 occur, but several technical difficulties must be overcome before 

 accurate measurements can be made. 



From a qualitative point of view, however, it would appear that 

 the contraction phase of the pigmentary response is limited by 

 pressure in a manner that parallels, at least roughly, the inhibition 

 of gelation which has been demonstrated in plasmagel systems 

 generally. It may be seen, for example, that the "half-expanded" 

 state of the chromatophore which occurs at about 2,500 Ibs./in.,- 

 corresponds to a gelation value of approximately 50 per cent, and it 

 seems probable that the other values, when they become available, 

 may likewise fall upon the general curve. 

 (2) Effects on pulsating chromatophore s 



In this other type of experiment the chromatophores were induced 

 to pulsate by the method-"* of Spaeth, '16, before the isolated scales 

 were placed in the pressure chamber and exposed to pressures of 

 1,000, 2,000, . . . 8,000 Ibs./in.- Immediately it becomes apparent 

 that the pressure imposes a limitation upon the "contraction phase" 

 of the pulsation. At 1,000 lbs. the pulsations continue, but although 

 the outward flow of the pigment granules is complete and reaches the 

 distal extremities of the numerous protoplasmic branches, the inward 

 flow is curtailed and a reversal of the direction of flow occurs before 

 the end of the procession of granules returning from each branch 

 quite reaches the control mass of the cell. At 2,000, 3,000, . . . 6,000 

 Ibs./in.,- a greater and greater reduction in the amplitude of the 

 pulsations is witnessed, but the reduction is due entirely to a 

 further and further curtailment of the inward flow, for the outward 

 flow continues to reach the distal ends of the branches. Finally, at 

 7,000 lbs. all pulsations cease, and while the pressure is maintained, 

 all of the melanophores remain in a fully expanded condition. When 

 decompression occurs, however, provided it has not been delayed 

 beyond some 25 minutes, the chromatophores immediately undergo 



