74 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



the muscle after the phase of shortening is past has been connected with this 

 latter process, namely, the oxidative destruction of the lactic acid, although 

 some authors contend that the lactic acid is not removed by oxidation to CO 2 

 and H 2 O, but is resynthesized to the sugar or the sugar-complex from which it 

 was derived. The heat produced in the oxidation is liberated in part as free 

 heat which warms the muscle, and in part may be stored in the muscle in some 

 form of potential energy, so that as an apparatus for the performance of 

 mechanical work the muscle is restored to its status quo ante. The theory has 

 many variations as regards details, but the central point is that the lactic acid 

 is the agent which causes the contraction by its action on the imbibition 

 properties of the fibril. The shortening in rigor mortis is explicable in the same 

 way as an acid effect.* 



* For various expressions of this theory, consult McDougall, "Journal of 

 Anatomy and Physiology," 31, 410, 1897, and 32, 187, 1898. Meigs, "Amer- 

 ican Journal of Physiology," 26, 191, 1910, and 22, 477, 1908. Fletcher and 

 Brown, "Journal of Physiology," 48, 177, 1914. Hill, ibid., 46, 28, 1913. 

 Pauli, " Kolloid-chemie der Muskelkontraktion," 1912. Fletcher and Hopkins, 

 Croonian Lectures, "Proceedings Royal Society," B. 89, 444, 1917. 



