100 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



Pressure. The characteristic action of pressure on the treppe heart 

 is to reduce the tension at low temperatures and increase it at high tem- 

 peratures (39, 40). When the relation between tension and temperature 

 is examined in detail (fig. 8) it is found that the general effect of com- 

 pression is to displace the tension curve to a higher temperature range. 

 At normal pressure, the tension rises with temperature to a maximum at 

 about 9° and thereafter diminishes. At progressively higher pressures, 



100- 



FiG. 8. Auricular tension in 

 relation to temperature and 

 pressure. 



8000 



6000 



UJ4000 



2000- 



5 10 15 



TEMPERATURE 



20 



Fig. 9. Temperature and 

 pressure necessary to produce 

 (A) the maximum tension in the 

 auricle, and (B) to produce re- 

 cession of the cleavage furrow in 

 the sea urchin egg by solation 

 of the cortical gel. 



15 



TEMPERATURE 



the maximum occurs at higher temperatures, but despite this shift the 

 maximum tension developed remains the same. An upper limit of tension 

 thus exists which is attained at a specific combination of temperature 

 and pressure. A plot of the temperature-pressure relation for equal and 

 maximum tensions is linear (fig. 9.4), the slope of the curve being pro- 

 portional to the entropy change of the system which could be calculated 

 provided the aV were known. 



For purposes of comparison, a similar relation is shown in fig. 9B 

 relating to the temperatures and minimum pressures which cause reces- 



