140 GKNERAL PROPERTIES OF LIVING TISSUES 



2. Make two cuts, 5 mm. apart, through the 

 frog's stomach at right angles to the long axis. 

 Hang the ring thus secured in the moist cham- 

 ber. Pass a bent hook through the lower end of 

 the ring, and attach it by means of a fine copper 

 wire to the hook on the muscle lever. Carry the 

 end of the copper wire to the binding post on the 

 muscle lever. 



Stimulate not more than twice with single in- 

 duction currents of a strength about the threshold 

 value for skeletal muscle of frog. 



There will be no contraction. 



Stimulate with galvanic current (two dry cells), 1 

 writing three curves, the duration of closure be- 

 ing approximately one-fifth second, one, and five 

 seconds, respectively. Compare the curves. 



The maximum shortening with currents of 

 brief duration (^ second) is very much less than 

 with currents of three or four seconds or over. 

 The briefer the current also, the quicker will the 

 maximum shortening be reached, and the quicker 

 will be the relaxation. 



3. If the galvanic current is very rapidly made 

 and broken, the muscle will not contract. 



1 If the muscle does not respond, wrap it with filter paper 

 moistened with normal saline solution, and wait until the tonic 

 contraction due to the cutting has passed off. The tonus may 

 sometimes be lessened by passing a galvanic current through the 

 preparation (p. 153). 



