ELECTROLYTES AND MUSCULAR CONTRACTION. 59 



with one having a value of 2t/[v(u -f z')] above the upper limit, a 

 solution could evidently be obtained which would sustain the heart- 

 beat. In this way many salt-antagonisms could be obtained. 

 Thus I have found that the heart of CcriodapJinia will not beat 

 in .V/ioKCl or in 20 c.c. .'V/ioNaCl -f 30 c.c. A'/io KC1, but 

 will beat in 30 c.c. A 7 'ioNaCl -f 20 c.c. TV/ioKCl, because the 

 two former solutions have values of ie'[i'(it + z')] lying above the 

 upper- limit for this rhythmically beating tissue, while the last- 

 mentioned solution has a value of ?//[z'(// + z')] lying between 

 the upper and lower limits. If we were considering the question 

 as one of toxicity, we should say that NaCl antagonized KC1. 

 The possible reason for the antagonism is now clear. 



1 1 . The values of the upper and lower limits for rhythmical 

 contractions in a tissue will obviously depend upon the constants 

 a and b for that tissue in the equation 



t = a- - + b. 



v(u + z') 



These constants will be different in different tissues, and need not 

 be the same for different parts of the same tissue. Thus, in the 

 case of Gonionemus, it is only necessary to suppose that the 

 limits for the center lie very close on either side of the value of 

 // [r'(// -+- z')] for NaCl, while the limits for the margin are some- 

 what farther apart, to obtain a possible explanation of the fact 

 that the center will beat in NaCl solution but not in NaCl solu.- 

 tion to which KC1 or CaCl., have been added, while the margin 

 will continue to beat in such solutions. 1 In this way many of 

 the apparently specific effects of certain ions upon rhythmically 

 contracting tissues may possibly be reduced to a general 

 explanation. 



12. Experiments will be continued with a view to obtaining 

 further evidence as to the existence of upper and lower limits in 

 the value of n.\_i'(ii -+- Z')], above and below which rhythmic 

 contractions are impossible, and also further experiments upon 

 the degree to which the crustacean heart obeys the formula 



// 



t = a- - + b. 

 v(u + z') 



1 Loeb, American Journal of Physiology, Vol. III. (1900), p. 383. 



