ELECTROLYTES AND MUSCULAR CONTRACTION. 57 



at 21 C., provided the different individuals are taken from the 

 same vessel, treated in the same way, and not previously exposed 

 to any extreme temperatures. With these precautions individuals 

 differing widely in development will be found to have practically 

 the same rate of heart-beat at 21. Ccriodaphnia can therefore 

 be used as homogeneous material for the investigation of the in- 

 fluence of electrolytes upon the rate of the heat-beat that is, 

 the constants a and b in the equation 



u 



, 

 v(u -f v) 



are practically the same for all the individuals, and the influence 

 of each solution can be tested upon a fresh individual. The 

 number of beats was registered upon a revolving drum by tapping 

 a key in a circuit containing a signal-magnet, and the time was 

 taken with a stop-watch. 



8. The following are the experimental results so far obtained, 

 the "time of one beat" meaning the interval between the begin- 

 ning of one beat and the beginning of the next. The values of 

 til\_v(u + i']\ are calculated from the table of ionic-velocities to 

 which I have previously referred. In every case the organisms 

 were first washed in tap-water, then placed in about 50 cc. of the 

 solution for 10 minutes and then placed, with a drop of solution, on 

 a glass plate kept accurately at 2 I by means of a stream of water 

 running underneath --in 10 minutes the rate of beat was noted. 



Solution. [z<(+-')] Time of one Value of a 



beat. when /'=i. 7232. 



A7ioLiNO 3 567.7X10-5 .3 sec. 356.4 



A'/ioNaCl 6ii.6Xio- 5 .150" 306.6 



Ringer 621. 2 X- 5 -183" 30.9 



too c.c. Ringer -+- 2 cc. A'/ioKCl 624.1 X IO ~ 5 - l8 5 " 35-75 



A'/ioMgCL, 631.4X10-5 .2 " 304.6 



40 c.c. A'/ioNaCl + 10 c.c. Njio KC1 645.9 X io~ 5 .238 " 303.7 



30 c.c. A7ioNaCl + 20c.c. A'/io KC1 677.8Xio~ 5 -353" 3 6 - 6 



30 c.c. A7ioLiNO 3 -(- 2oc.c. A 7 /ioNH 4 CNS 725.1 X io- 5 -375" 289.4 



A'/ioNH 4 CNS 937.6X10-5 .5 " 237.1 



Thus we see that the value of a is constant for values of 

 ul\_i>(n -I- f ')] between and including 6 1 1.6 x io~ 5 and 677. 8x io~ 5 . 

 Above and below those values it is variable. 



9. It is evident that upper and lower limiting values of 

 ji/[i'(n -f ?>)] exist between which sustained beats are possible. 



