148 The Structure of Protoplasm 



a complete and vigorous "contraction," and within about 3 minuiei;, 

 full pulsations have been resumed. 



(3) Coraparison between pseudopodia and the branches oj a pig- 

 ment cell 



One further observation may be added to the evidence which 

 indicates that the effects of the pressure are being mediated through 

 solational changes similar to those which have been demonstrated 

 in other cases. At pressures of 7,000-8,000 Ibs./in.- occasionally it 

 may be seen that one of the several elongate protoplasmic processes 

 which radiate out from a particular melanophore becomes pinched 

 off, losing its connection with the central portion of the cell at a 

 greater or lesser distance from the origin. Such isolated portions of 

 the cell become rounded into a discrete mass while the higher 

 pressure is maintained, but show abortive attempts at "expansion" 

 and "contraction" when the pressure is reduced. 



This observation indicates that the branches of the unicellular 

 chromatophore are in a sense comparable to the pseudopodia of the 

 amoeboid cell and that a reorganization of the elongate form may 

 occur when a profound solation of the protoplasm is induced. The 

 greater resistance in the case of the chromatophore may be due 

 largely to the fact that its branches are not free, but rather extend 

 out into the interstices between the other tissues (see Matthews, '31) . 

 Under such conditions, no doubt, the chromatophore branches receive 

 additional support, from contact with (or attachments to) the sur- 

 rounding cells, and this support is sufficient, in most cases, to prevent 

 collapse even in periods of complete protoplasmic liquefaction. 



IV. CELLULAR ACTIVITIES WHICH DO NOT INVOLVE 



A very brief and fragmentary consideration of the many experi- 

 ments which have dealt with the effects of pressure upon the physio- 

 logical activity of muscle, nerve, cilia, and flagella may suffice to show- 

 that this group of phenomena must be considered in a separate 

 category. The physiological activities which already have been 

 considered at length display certain common attributes. All are 

 progressively inhibited throughout the entire physiological range of 

 pressure, and in all cases, the degree of inhibition appears to be in 

 proportion to the suppressing action of pressure upon the formation 

 of protoplasmic gels. In contrast to this, the physiological activities 

 which remain for consideration are not inhibited, but rather are 

 augmented in the lower portion of the pressure range, and further- 

 more, no clear relationship has been demonstrated between the 



