A. J. CARLSON 567 



loth in the Molluscs and the Arthropods. — The paralysis of the inhib- 

 itory nerves may be only temporary, their function being restored 

 by bathing the heart in blood. The paralysis is not produced except 

 by a concentration of the drugs that causes marked primary accelera- 

 tion of the heart rhythm. I did not find any essential difference in the 

 paralyzing action of the three alkaloids. 



In the lamellibranchs {Tapes, Venus) the curare solution may act 

 for 20 to 30 minutes before the action of the inhibitory nerves on the 

 heart is abolished. In Helix and Limax the action is much quicker, 

 or in 4 to 8 minutes. The action is quicker the stronger the solutions. 

 In Loligo the injection of a few drops of 0.5 per cent curare or atropine, 

 or 0.1 per cent nicotine in the cephalic vena cava paralyzes the cardio- 

 inhibitory nerves in 4 to 5 minutes. I have not succeeded in restor- 

 ing the function of the nerves in Loligo after this paralysis. In 

 Limulus the concentration of the drugs must be sufficient to cause 

 great augmentation of the rhythm in order to abolish the influence 

 of the inhibitory nerves on the heart, in which case the paralysis is 

 brought about in a few minutes. In weaker solutions it requires much 

 longer time and may in fact not occur at all. 



At what point do these alkaloids act to produce the paralysis of the 

 cardioinhibitory nerves? Atropine paralyzes the vagus fibers in the 

 vertebrate heart, and it is generally held that this action is on the in- 

 hibitory nerve endings in the muscle. Nicotine, on the other hand, is 

 supposed to paralyze the synapses of the vagus fibers with the in- 

 hibitory ganglion cells in the heart. Turning now to the heart of 

 Limulus, it is certain that atropine as weU as curare and nicotine act 

 on the ganghon in order to paralyze the inhibitory nerves. If the 

 action of the drugs is confined to the heart muscle and the nerves and 

 the nerve endings in the muscle no paralyzing effects are produced. 

 It would therefore seem that the action of these alkaloids, in abolish- 

 ing the action of the inhibitory nerves on the heart, is on the ganglion 

 cells in the heart or on the endings of the inhibitory nerves in connec- 

 tion with these cells. 



While it is certain that curare, atropine, and nicotine in sufficient 

 concentrations paralyze the cardioinhibitory nervous mechanism in 

 molluscs and arthropods, this action requires, on the whole, a greater 

 concentration of the drugs than that sufficient for the paralysis of the 

 cardiac vagi in the vertebrates. 



