564 THE OUTGO OF ENERGY 



through their processes to the muscular fibres of 

 the heart. 



Atropine. With a clean pipette apply a few 

 drops of a solution of atropine (0.5 per cent) to 

 the heart. After a few moments lift the ventri- 

 cle and stimulate the crescent. 



The heart is not inhibited. Atropine paralyzes 

 the intracardiac inhibitory nerves. 



Muacarine. With a tine pipette put upon the 

 ventricle a few drops of normal salt solution con- 

 taining a trace of muscarine (a poisonous alkaloid 

 extracted from certain mushrooms). 



The ventricle will gradually be arrested in 

 diastole, much distended with blood. 



Antagonistic Action of Muscarine and Atropine. 

 With a fresh pipette apply a little normal salt 

 solution of atropine (0.5 per cent). 



The heart will commence to beat again. 



THE CENTRES OF THE HEART NERVES 



It has been shown that the heart receives in- 

 hibitory and augmenting nerve fibres. The sit- 

 uation of the inhibitory and augmenting " centres," 

 i. e. y the nerve cells from which the inhibitory 

 and, augmenting fibres spring, should now be 

 considered. 



Inhibitory Centre. Place a frog and a small 

 sponge wet with ether under a glass jar. Be very 



