112 INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



complete solation of the plasmagel structure of these cells occurred when 

 they were exposed to increasingly high hydrostatic pressures in the range 

 up to 8000 Ib/in^. This result was difficult to understand until Freundlich 

 (4) published his analysis of gelational phenomena. Then it was realized 

 that protoplasmic gel systems, of which quite a number have now been 

 studied (21), are uniquely different from such more familiar types as 

 gelatin or agar. Instead of solating when warmed, protoplasmic gel struc- 

 tures become more firmly set; and when higher pressures are applied, 

 cellular gel structures are weakened and eventually solated — which is 

 just opposite to the behavior of the gelatin system (23). In short, since 

 protoplasmic gelations are endothermic and since a volume increase (AV) 

 is involved, the sol-gel equilibrium is shifted toward the right by in- 

 creasing temperature, and toward the left by increasing pressure. Thus 

 both temperature and pressure have provided useful tools not only for 

 analyzing the functional significance of intracellular gelations, but also 

 for study in the metabolic processes which supply energy to these re- 

 actions. The molecular theory of volume changes accompanying various 

 biological processes is discussed at some length in Johnson, Eyring and 

 Polissar (7). 



Special Techniques and Apparatus. Direct observation of the living 

 specimens during exposure to high pressure is most essential. Character- 

 istically the effects of pressure are rapidly and completely reversible 

 and in several instances earlier workers obtained erroneously negative 

 results simply because their observations were delayed until after de- 

 compression, following the removal of the material from the pressure 

 chamber. Conseciuently progress in the field was greatly facilitated by 

 the development of a microscope-pressure chamber in which small organ- 

 isms and individual cells may be subjected to pressures up to 15,000 

 lb/in.- (22, 21). Also the development of the pressure-centrifuge (1) and 

 of an adaptable temperature control housing (21) were equally important. 

 This equipment, in fact, has made it possible to obtain centrifugal meas- 

 urements of the gelational state of the cytoplasmic components of different 

 cells under systematically varied conditions of temperature and pressure 

 throughout the physiological ranges, and to relate these gelational meas- 

 urements to the observed changes in the activity and behavior of the 

 cells. 



Measurements of the relative gel strength have now been made on a 

 number of different cells, including two species of amoeba (2) two species 

 of Arbacia (1, 17, 18), and Elodea canadensis (19); and the consistent 

 pattern of all these data tends to justify the assumptions upon which 

 the method is based. 



