Protoplasmic Streavung — Relation to Gel Structure 149 



physiological effects and the effects of the pressure upon the physical 

 characteristics of protoplasmic gel systems. 



A. MUSCULAR CONTRACTION 



The marked increase in the tension developed during a single 

 isometric contraction^" at pressures between 100 and 6,000 Ibs./in.^ 

 was reported, first for cardiac muscle (Edwards and Cattell, '27) 

 and then for skeletal muscle (Cattell and Edwards, '28) . For cardiac 

 muscle the maximum augmented tension is four to six times greater 

 than the atmospheric value and occurs at about 6,000 Ibs./in.- 

 (Edwards and Cattell, '30). For skeletal muscle, however, the 

 maximum additional tension is only 20-40 per cent greater than the 

 atmospheric value and is reached at pressures between 2,000 and 

 4,000 Ibs./in.- (Cattell and Edwards, '32) . 



The pressure effect on tension in both cardiac and skeletal muscle 

 varies, however, markedly with temperature. In fact, a reversal of 

 sign occurs, at 5-8° C. for cardiac muscle (auricular muscle of the 

 turtle. Brown, '34a), and at 9-14° C. for striated muscle (sartorius 

 muscle of the frog, Cattell and Edwards, '32) . Below these critical 

 points a depression of tension occurs throughout all of the physio- 

 logical pressure range. 



Brown ('36) has observed that the full measure of additional 

 tension is obtained only when the period of compression antecedes 

 the moment of stimulation, and that no extra tension is obtained 

 unless the compression intervenes before the first one-eighth of the 

 contraction has been completed (Fig. 9) . In fact, when the period 

 of compression is confined to the remaining seven-eighths of the 

 contraction phase, the tension amounts to less than the atmospheric 

 control value (Brown, '34b and '36) . 



B. CONDUCTION OF THE NERVE IMPULSE 



Grundfest and Cattell ('35) have demonstrated clearly that the 

 compression effects on the nerve impulse do not constitute a simple 

 case of progressive inhibition. These observations, on the form and 

 magnitude of the spike potential and on the rate of propagation, 

 were recorded by means of a cathode ray oscillograph, utilizing 

 grouped A fibres of the frog sciatic nerve, and in some cases, single 

 fibres of a sciatic-peroneal preparation. 



The effects of moderate compression (below 5,000-6,000 Ibs./in.^) 



