128 The Structure of Protoplasm 



a suctorian^ (Ephelota) , in Paramecium,^ and in human erythro- 

 cytes.^ Among the plants a similar effect has appeared in the leaf 

 cells of Elodea,'' in the plasmodium of Physarum," and in the cells 

 of Spirogyra.^ 



A number of the cases have yielded quantitative measurements, 

 and these indicate that the relative magnitude of the liquefaction 

 induced by pressure is the same in all cases, regardless of whether 

 the initial gel at atmospheric pressure is quite firm or is relatively 

 fluid. Each increment of 1,000 Ibs./in.- reduces the rigidity by almost 

 25 per cent. Furthermore, within fairly broad limits, the effect is 

 reversible. Pressures up to 4,000 Ibs./in." may be maintained for 

 about an hour, and yet, when the cells are returned to atmospheric 

 pressure, the original structural characteristics of the gel are 

 i-estored within a minute, or perhaps within an even shorter time. 

 For higher pressures irreversible changes begin to appear much 

 sooner, depending upon the intensity. 



B. STATEMENT OF THE PROBLEM 



Since it is known that pressure induces solation, or conversely, 

 that pressure prevents gelation from occurring in protoplasmic 

 systems, a useful tool has been provided for analyzing the role of 

 such phenomena in various forms of physiological activity. At the 

 present time quite a number of studies are available, and the pur- 

 pose of this paper is to determine, so far as is possible, how the 

 manifold physiological effects of pressure may be related to changes 

 in the sol ^ gel equilibrium. 



C. STREAMING ACTIVITIES IN CONTRAST TO OTHER PHYSIOLOGICAL 



PROCESSES 



Perhaps a general statement of the results, made in advance of 

 the detailed account, will provide a useful orientation. In general, 

 it seems valid to say that one group of physiological activities, the 

 group in which protoplasmic streaming is the common attribute, 

 appears to be particularly vulnerable to inhibition by very moderate 

 (below 5,000 Ibs./in.-) intensities of compression. This pressure- 

 susceptible group includes amoeboid movement, cyclosis, cell division 

 (in animal cells) , and the migration of pigment in the unicellular 

 type of chromatophores. 



A second group of activities, which includes contraction in muscle, 

 conduction in nerve, and the motility of cilia and flagella, is not 

 inhibited by moderate pressures. In fact, the characteristic activities 



