72 ELEMENTARY PHYSIOLOGY. XII. 



auricle.) Arecoline, muscarine and atropine act on the 

 endings of the post-ganglionic fibres and on the heart 

 muscle. 



5. The action of these poisons may be determined in the follow- 

 ing way. After cutting away the pericardium, and severing the liga- 

 ment of the ventricle, the aortse are cut through, and holding the 

 heart up by these, the superior vense cavfe are cut through and a 

 ligature tied round the inferior vena cava and surrounding tissues 

 close to the liver; the ends of the thread are tied to make a short 

 loop. The extreme tip of the ventricle is clamped as in 1. The heart 

 is cut out and suspended in the muscle chamber (Fig. 22) which is 

 filled with saline solution and a tracing of the heart beat taken. 



The vessel is then lowered, a watch-glass put on it, and a drop or 

 two of -5 p.c. arecoline dropped on the heart. When the heart beat 

 has stopped the watch-glass is taken away and the vessel raised so 

 that the heart is in saline solution. 



In a minute or two, the vessel is again lowered, another watch- 

 glass placed on it and 1 p.c. atropine dropped on the heart. 



See also Less XIII, 1. 



DEMONSTRATIONS. 



1. Current of action of the frog's heart. 



2. The string galvanometer. 



