104 ELECTRO-PHYSIOLOGY CHAP. 



Preyer, affirmed that hard-frozen muscles were still able to con- 

 tract on thawing, and Waller finds the same for cardiac muscle. 

 But in all these experiments it is questionable whether the 

 contractile substance itself, or only the interstitial fluid, freezes. 



VI. EFFECT OF CHEMICAL SUBSTANCES UPON MUSCULAR 

 CONTRACTION 



The normal manifestations of muscular activity always betray 

 more or less fundamental disturbance, when the chemical relations 

 of the contractile elements undergo any material alteration. 

 This appears already from the experiments we have been dis- 

 cussing, and in this connection the study of fatigue phenomena, 

 which undoubtedly depend in part on the accumulation of certain 

 disintegration products, is very instructive. Without entering 

 into the action of all the many bodies whose effect on muscular 

 excitability has so far been tested, we may quote some very 

 cogent facts that are of importance to the sequel. In the first 

 place, we must mention the curious and striking antagonism 

 in the physiological action of the salts of sodium and potassium, 

 which are in such close chemical affinity. Weak solutions of NaCl 

 (0'5 0'6 / ) have long been employed where a fluid is re- 

 quired to preserve the striated and smooth muscles, as well as the 

 nerves, of vertebrates for as long as possible in approximately normal 

 conditions. We are so accustomed on the strength of repeated 

 experiences to regard "physiological salt solution" -the con- 

 centration of which must, of course, be adjusted to the content of 

 salt in the tissue, and must therefore be correspondingly greater 

 for sea-animals as .a perfectly neutral fluid, that it may well 

 surprise us to learn from F. S. Locke's recent observations (66) 

 that this is only true to a limited extent, even in striated frog's 

 muscle. In experimenting with normal preparations of sartorius, 

 and with preparations that had been lying for a long time in 

 0'6 / NaCl solution, he found considerable differences in ex- 

 citability and curve of contraction. Single induction currents of 

 great strength (" break " shocks in particular) sent through the 

 entire muscle produced in salt muscles " tetanic contractions of 

 enormous height and a duration of several seconds, after which the 

 muscle relaxed suddenly, and showed only a slight contraction 

 residue." S. Einger (67) had previously observed an inclination to 



