TEMPERATURE AND EFFICIENCY 141 



That is 



(I.) The dissociation of lactic acid, the setting free of H ions, 

 is increased in rate and extent by increase in temperature (Chap. 



VII.). 



(II.) No change known. 



(III.) Temperature increase causes increase of salt de-adsorption. 



(IV.) No change known. 



(V.)' Because of the increased dissociation of salts by the 

 increase in temperature and because of the increased kinetic 

 energy of water seeking admission the rate of endosmosis will 

 increase with increase in temperature. 



These have all to be restored to precontraction state, and there- 

 fore do not materially contribute to this part of the discussion. 

 But the temperature coefficient of contraction is negative, there- 

 fore all these reactions must fall within the phase of restitution. 

 Experimentally it has been found that this phase increases in rate 

 with temperature. (The other effects of temperature on muscular 

 contraction will be dealt with later. Just now we are concerned 

 with isolated muscle.) A moderate increase of temperature 

 thus increases the removal of lactic acid and the restoration of 

 potential energy to the muscles, while not appreciably lessening 

 their power to transform potential into kinetic energy, i.e. to 

 contract. . Further, it has been shown by Lagrange that an in- 

 crease in temperature increases the efficiency of muscle. Lately, 

 workers have ascribed this increased efficiency to the more rapid 

 removal of lactic acid. 



Now we have seen that : 



(a) The restitution phase is accompanied by an increase in the 

 temperature of muscle. 



(b) The rate and efficiency of contraction is reduced by increase 

 in temperature, and 



(c) The rate and efficiency of restitution is increased by increase 

 in temperature. 



It therefore follows that there will be a temperature at which 

 muscle work (contraction and restitution) will be performed most 

 efficiently. Further there will be an optimum speed at which 

 work will be carried out. This speed will be regulated 



(1) By the natural rhythm of contraction of the muscle 

 depending on the length of the contractile body (Fig. 25). 



(2) By the optimum temperature, and 



(3) By the amount of resistance that has to be overcome in 

 shortening. (See also Chap. XXVIII.) 



