236 



PHYSIOLOGY 



THE ACTION OF DRUGS 



Of the drugs that have a direct action on muscle, the most remark- 

 able is veratrin, which causes an excessive prolongation of a muscular 



B 



FIG. 70. A. Tracin'g of the contraction of a frog's sartorius, poisoned with 

 veratrin, in response to a momentary stimulus. The time-marking 

 Indicates seconds. 



B. Tetanic contraction of normal sartorius in response to rapidly 

 interrupted stimuli. (The duration of the stimulus is indicated by the 

 words 'on 1 and 'off/) It will be noticed that the two curves are 

 practically identical. (Miss BUCHANAN.) 



contraction (produced by a single stimulus). Thus the ' twitch ' of 

 a muscle poisoned with veratrin may last fifty or sixty seconds, instead 

 of the normal one- tenth of a second (Fig. 70). 



Barium salts have a similar, though 

 less marked effect. 



In order to carry out the poisoning 

 with veratrin, very weak solutions (1 in 

 100,000 or 1 in 1,000,000 of normal 

 saline) should be used and the muscle 

 exposed to its action for some hours. 

 We get then on a single stimu- 

 . Excitation. ms a response lasting many 

 ' seconds. seconds and exactly similar in 



FIG. 71 Tracing of the contraction of a height and form to a tetanus 

 muscle poisoned by the injection of a ,.,,,. 

 strong solution of veratrin, showing the Obtained by discontinuous stimil- 



donlito orataoHon due to unequal poison- lation. If stronger solutions be 

 mg of different fibres. (BIEDERMANN.) . 



used, the action of the drug is 



apt to affect the fibres unequally, so that we may have a sharp normal 

 twitch preceding the prolonged contraction (Fig. 71). If the muscle 

 be excited immediately after the prolonged contraction has passed 

 away, it responds with a single twitch like a normal muscle, but if 

 allowed to rest a few minutes, stimulation is again followed by the 

 peculiar long-drawn-out contraction. 



