ELEMENTARY EXPERIMENTAL PHYSIOLOGY 219 



muscle thrown into contraction voluntarily, or involuntarily as in 

 shivering. 



(a) The Incomplete Tetanus produced by Strychnine. The cerebral 

 hemispheres of a frog are destroyed by com- 

 pression with a pair of small pliers or Spencer 

 Wells forceps, and then the gastrocnemius 

 muscle is prepared with the circulation intact. 

 A piece of string is placed under the gas- 

 trocnemius muscle and is then tightly tied 

 round the upper portion of the tibio-fibula 

 and the remaining muscles ; the leg is now 

 cut away below the ligature. In this manner 

 haemorrhage is prevented, the circulation in ^^^^^^^^^_ 

 the muscle is intact, and the muscle is free to | 



move with each contraction. A strong pin is 

 placed through the lower extremity of the 

 femur and is pushed firmly into the cork of 

 the myograph ; a piece of moist flannel is 

 pinned down over the body of the frog in ; 



order to prevent the contraction of the 3 



muscles of the trunk and limbs from disturb- _ fe 



ing the lever connected with the gastro- 

 cnemius muscle. 



Strychnine is sparingly soluble in water, 

 1 in 6700, but a dose of 10-15 minims 

 (0-592 - 0-888 c.c.) of a saturated solution of 

 the drug in normal tap-water saline solution 

 will in a frog produce the characteristic con- 

 vulsions and death. Such a dose is injected 

 under the skin of the frog's back. Twitches -I 



and convulsions soon begin and the contrac- * 



tions of the gastrocnemius muscle are recorded 

 simultaneously with the movements of a 

 signal marking seconds (Fig. 206). The I 



number of contractions is about 8 or 10 per 



second. This is a measure of the rate of dis- | ; 



charge of the nervous impulses from the 

 nerve-cells of the spinal cord. The stage of 

 incomplete tetanus is followed by prolonged 

 twitches or clonus. If the spinal cord be 

 destroyed by a probe during the stage of 

 tetanus the contractions will cease at once, 



