110 



PRACTICAL PHYSIOLOGY 



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

 drops of nitrate of musoarine (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 O5% solution of atropine sulphate. 

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



FIG. 108. Frog's heart. 1, Normal ; 2, three minutes after one drop of 10% solution 

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

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



increasing amplitude. Muscarine 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, Jor atropine 

 paralyses the post-gajgl j^njjsfibres of this nerve.) The effect of atropine 

 cannot be antagonised by a further application"^ muscarine. 



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

 atropine acts as its antagonist. 



Muscarine is an alkaloid obtained from the poisonous Fly Agaric a 



