ELEMENTAEY EXPERIMENTAL PHYSIOLOGY 



71 



(2) the crescent. Next with a glass pipette apply to the heart a few 

 drops of nitrate of musearine (10% solution). The tone, frequency, and 

 amplitude of the heart will decrease until at last the heart becomes 

 arrested in diastole. Mechanical excitation may still excite the heart 

 to give a single contraction. 



Now apply some drops of a 0-2 0'5% solution of atropine sulphate. 

 The heart will begin to beat again, at first feebly, and then with 



FIG. 72. Frog's heart. 1, Normal ; 2, three minutes after one drop of 10% solution 

 of musearine ; 3, after the application of a weak solution of atropine sulphate. The 

 time is marked in seconds. (Pembrey and Phillips.) 



increasing amplitude. Musearine abolishes the tone, rhythmic power, 

 and conductivity of heart muscle, while atropine has in each respect the 

 antagonistic action. This experiment succeeds on any ganglion-free 

 strip of tortoise heart. After the application of atropine, excitation, 

 either of the vagus or of the crescent, is ineffectual, for atropine 

 paralyses the post-ganglionic fibres of this nerve. The effect of atropine 

 cannot be antagonised by a further application of musearine. 



A 1% solution of pilocarpine acts in the same way as musearine, and 

 atropine acts as its antagonist. 



Musearine is an alkaloid obtained from the poisonous Fly Agaric a 



