368 PROTOPLASMIC ACTION AND NERVOUS ACTION 



substance. The contraction then resulting is much 

 more rapid and vigorous than in the control muscle which 

 is brought into the same solution directly from Ringer; 

 the degree of permanent shortening is also greater, as is 

 also the degree of coagulation of the muscle protoplasm, 

 as shown by the whitening or opacity produced. The 

 action of contraction-producing salt solutions Uke KCl, 

 Na tartrate, sulphate, and citrate is similarly intensified 

 by a previous bath of the kind above; also the rapidity 

 of onset of heat-rigor, with the associated contraction, 

 when the muscle is dipped in warm Ringer's solution 

 (38'-40°). These sensitization-effects have been demon- 

 strated with the following cytolytic substances: chloro- 

 form, cytolytic glucosides (saponin, digitahn, aconitin, 

 and agaricin), tetanus toxin, rattlesnake venom, foreign 

 blood sera (horse, dog), and soaps. The degree of the 

 stimulation following the introduction of the salt- 

 sensitized muscle into the solution, as indicated by the 

 rate and degree of the contraction, is in general pro- 

 portional to the intensity of the cytolytic action (as 

 shown by varying the concentration and nature of the 

 cytolytic substances) .^ 



Since in all such experiments the contraction follows 

 immediately (within a second or less) after placing the 

 muscle in the stimulating solution, there seems to be no 

 doubt that the initiatory effect consists in an alteration 

 of the external surface layer of the muscle cells. Appar- 

 ently, when the normal muscle is exposed to the pure 

 salt solution, the cell surface is rendered more susceptible 

 to alteration by external chemical agents, and the 

 susceptibility to chemical stimulation of the kind above 



^American Journal of Physiology, XXVIII (1911), 197; cf. p. 214. 



