208 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



tain this new level was recorded. By changing the level of the new mem- 

 brane potential step by step, a measure of the membrane resistance was 

 obtained. 



Measurement of Membrane Impedance During Activity. An A.C. 



impedance bridge was constructed, one arm of which consisted of the squid 

 axon membrane and a pair of electrodes (one inside and the other outside 

 the axon). The internal electrode was a 100 fx silver wire with its enamel 

 coating removed for a length of about 10 mm. The ratio arms of the 

 bridge consisted of a pair of fixed resistors, one 10 ohms and the other 

 either 100 or 300 ohms. The bridge was balanced by varying the resistance 

 (0-300 kilohms) and the parallel capacity (0-200 ju/xf ) in the third arm of 

 the bridge. The frequency of the bridge A.C. was 20 (sometimes 10) kc 

 per sec. 



METHOD USED FOR APPLICATION OF PRESSURE TO NERVE FIBER 



Hydrostatic pressures up to 16,000 psi were developed by the use of a 

 hand-operated hydraulic pump (fig. 3). The reaction vessel (pressure 



COLO JOINTS AND 

 MICROVOLTMETER 



n. 



REGULATED 

 TEMPERATURE BATH 



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NICHROMC 

 HEATING WIRE 



OIL 

 RESERVOIR 



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( PUMP > 



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FiG. 3. Experimental set-up used for applying high hydrostatic pressures to the 

 nerve fiber. A: superpressure tubing connecting pump to interior of reaction vessel; 

 B: self -sealing electrical connectors between inside and outside of reaction vessel; 

 E: steel thrust ring; F: inner pressure head; G: 'delta' type steel gasket; H: coils 

 made of superpressure tubing for circulating hot or cold fluid through the interior of 

 the reaction vessel; /; outside cap screwed on to body of vessel (The cap was equipped 

 with 16 thrust bolts); J: body of reaction vessel; A'.- bridge-insulator. 



