DUGALD E. S. BROWN 



103 



control (fig. 10-4, 11). It is clear that, during a brief period following 

 stimulation, a process occurs which is augmented l)y pressure and which 

 basically determines the tension to be developed. The pressure-effective 

 period begins at stimulation and is 80% completed by the end of the 

 latent period. 



The converse of this experiment involves compression of the muscle prior 

 to stimulation followed by abrupt decomjiression when about one-fifth 

 tension has developed. The result of such a decompression is that further 

 development of tension ceases, while the tension already developed is 

 sustained until relaxation intervenes at the normal time. This experiment 

 shows that although compression during the latent period is necessary in 

 order to augment the tension, compression also must be maintained 



AURICLE 



Fig. 11. a plot of the total 

 ten.sion developed when the 

 abrupt compression is applied 

 progressively later in the con- 

 traction cycle. Compression at 

 the broken line and thereafter 

 sustained has little effect on 

 tension. Conduction time, 0.1 

 seconds. 



4000 psi 



during the contraction phase for full tension to develop. From this result, 

 it is inferred that the conditions which are set up by pressure during the 

 latent period, and which are essential for a greater tension, disappear 

 rapidly on decompression. In view of the large decrease in volume of 710 

 cc/mole, it is concluded that the process involved is the production and 

 disappearance of the activator d. In Goodall's terminology, Cd estab- 

 lishes the activation charge which determines the rate of development 

 of tension and, in the twitch, the duration of the active state. 



At low temperatures where the major effect of pressure is one of 

 inhibition, the use of an abrupt compression provides information on the 

 sequence of events. At 5°C the twitch under a sustained pressure is smaller 

 and relaxation is slowed (fig. 12C, P). An abrupt compression, inter- 

 posed after the initial one-fifth of the contraction is completed, causes 

 a small abrupt fall in tension, a smaller peak tension finally developing 

 (fig. 12-1). As evidenced by the larger tension developed under a sus- 



