84 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



C 



Cd 



AMi- 



depolarization 



-P (D) 



C ) 



(A) 



(B) 



U) 



contraction 



~P (E) 



IC ) 



tenth of the contraction phase. In time this coincides approximately with 

 the latency relaxation of Sandow (5) and the development of the alpha 

 state as determined by the abrupt application of high hydrostatic pres- 

 sures (6) . Since AMar^ is fully formed practically by the end of the latent 

 period, shortening and the performance of work depend on reaction B in 

 which relaxed AMa/ passes to the contracted state AMa/. 



Hill considered that this reaction was independent of changes in tension 

 or length and proceeded merely as a function of time. In subsequent studies 

 on this reaction in the tetanus by investigating the relation between the 

 rate of shortening under different loads, Hill described the fundamental 

 relation 



(P + a)v = b(Po - P) 



where Po is the maximum tension, P the load, v the rate of shortening, b a 

 constant approximating a rate of energy liberation and a has the dimension 

 of a force. The constants a and b, although critically described, remain to 

 be identified with specific physico-chemical events in contraction. 



Polissar (7), in an attempt to give further meaning to the fundamental 

 equation, has proposed a dynamic contractile mechanism in which con- 

 tractile units in the long ('L') state go over through a reaction sequence 

 (I) to the short ('S') state from which they can return, though by a 

 different pathway (II) , to the long state. The reactions (I) predominate in 

 shortening whereas the reactions (II) predominate in relaxing, and a 

 tetanus reflects a steady state of (I) and (II). 



The foregoing considerations of Hill and Polissar relating to the sartorius 

 of the frog clearly relate to the development of tension by the fully acti- 

 vated unit AMa/'. In other muscles, however, notably the retractor penis 

 of the turtle, there is evidence that the rate of development of tension 

 is governed in part by the rate of development of the active state. Thus 

 Goodall (8) has shown that in this muscle the rate of development of 

 tension in a tetanus is at least ten times slower than the rate of redevelop- 



