154 PRACTICAL PHYSIOLOGY 



to the heart a few drops of nitrate of muscarine (10 per cent, solu- 

 tion). 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 per cent, solution of atropine 

 sulphate. The heart will begin to beat again, at first feebly, and 

 then with increasing amplitude. Muscarine abolishes the tone, 

 rhythmic power, and conductivity of heart muscle, while atropine 



FIG. 145. Contraction of the frog's heart. 



I . Normal heart-beat, II. and III. poisoned by nicotine. The downstroke represents contraction. 

 The time is marked in seconds. (L.H.) 



has in each respect the antagonistic action. This experiment suc- 

 ceeds on any ganglion-free strip of the heart of the tortoise. 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 muscarine (Fig. 143). 



A 1 per cent, 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 



