564 ACTION OF CURARE, ATROPINE, AND NICOTINE 



the blood of Limulus has a powerful stimulating action on the gan- 

 glion cells in the heart. The solution of these drugs in the isotonic 

 solvents changes the osmotic pressure of these liquids and a sHght 

 change in the osmotic pressure of the blood has itself an effect on the 

 heart. 



The point of the action of these alkaloids in the heart is not yet 

 known. On the myogenic theory of the heart beat their stimulating 

 effects may be due to action on the accelerator nervous mechanism or 

 to a direct action on the heart muscle. On the neurogenic theory 

 the augmentation of the rate of the beats can hardly be accounted for 

 except by direct action on the local ganglia, while the increased am- 

 pHtude of the contractions may be due to action directly on the 

 muscle. To answer the question whether these and other alkaloids 

 act on the nervous or on the muscular tissue in the heart or on both, 

 several investigators have studied their action on the embryonic heart 

 on the theory that the heart on the embryo begins to beat before any 

 nervous elements are present. Pickering (1893, 1894-95) found 

 that atropine and nicotine accelerate the embryonic (chick) heart, 

 while strong solutions of atropine depress the rhythm without any 

 primary stimulation. Cyrillo (1901) states that atropine depresses 

 the embryonic heart. This investigator finds, moreover, that the 

 action of the principal alkaloids on the embryonic heart is the same as 

 on the heart of adults, from which he concludes that these drugs act 

 primarily on the heart muscle, their action on the nervous tissue in 

 the heart being entirely of a secondary character. 



I have come to the very opposite conclusion, or that the primary 

 action of the alkaloids is on the gangHon cells in the heart and not on 

 the muscle. This conclusion is based on the results on the heart of 

 Limulus (Carlson, 1906-07). For this Hne of study the Limulus 

 heart is prepared in the following manner : 



The nerve cord on the dorsal side of the heart is extirpated in the 

 first three segments, which leaves this part of the heart free from 

 ganglion cells, the rhythm being maintained by the impulses reaching 

 the muscle from the nerve cord of the middle third of the heart along 

 the lateral nerves. It is desirable to isolate further the ganglionated 

 and the ganglion-free ends of the heart by excision of the heart muscle 

 for a distance of 1 cm. in the third segment. This dissection can be 



