104 INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



tained pressure, the compression at this temperature is also increasing the 

 degree of activation (fig. 12-P, as compared to fig. 12-1). The additional 

 fact revealed, however, is that the state of tension, once developed, is 

 abruptly reduced by compression with a reduction in volume of about 

 120 cc/mole (fig. 12-2). The effect is reversible, a decompression at 

 peak tension causing a very rapid redevelopment of tension (fig. 12-4). 

 Treppe Phenomenon. In the preceding discussions the treppe heart 

 is dealt with. The phenomenon of treppe itself deserves consideration. The 

 low tension in such a heart at 20°C can be increased by repetitive 

 stimulation and at a suitable frequency attains the j^lateau tension. This 



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Fig. 12. Myograms of the turtle auricle at 5°C showing the effects of an abrupt 

 compression applied during the contraction cycle. Myogram C, the control at atmos- 

 pheric pressure; myogram P recorded at 4,000 psi. In myograms 1, 2 and 3 an abrupt 

 compression to 4,000 psi is interposed as indicated. Myogram 4 recorded at 4,000 psi 

 with an abrupt decompression interposed at the time of peak tension. The slow and 

 prolonged contraction results from a re-excitation of the tissue by the decompression. 



has long been recognized as the treppe, or staircase, effect. Recently, 

 Twente (37) has shown that such a muscle in full treppe is practically 

 insensitive to pressure. Moreover, the resting muscle could be brought 

 to full treppe tension within 10 rather than the usual 75 contractions, 

 provided it was compressed during only the initial one-fifth of each 

 contraction phase. In the light of the preceding results, it would appear 

 that the treppe phenomenon depends on changes in the amount of activator 

 Cd that has been formed at the onset of contraction. This seems particularly 

 important in relation to the possible locus of action of Ca++ and other 

 agents which eliminate treppe. It is noteworthy that in muscles which 

 normally do not produce treppe, and where at 20°C the plateau tension 

 develoi)s, pressures up to 10,000 psi do not alter the tension. In this 

 case activation either does not play a significant part or is diminished 



