A. J. CARLSON 561 



My experiments on several classes of molluscs with the view of paralyz- 

 ing the motor nerve endings in the muscle by atropine have yielded 

 uniformly negative results. So far, then, we know of no drug that 

 will paralyze the motor nerve endings in invertebrates without ma- 

 terially depressing the muscle itself, after previous paralysis of the 

 central ganglia. 



2. The Action of Curare, Atropine, and Nicotine on the Heart 



Rhythm. 



A review of the Hterature on the action of the alkaloids on the in- 

 vertebrate heart discloses considerable disagreement between the 

 results of different observers. Ransom (1884) found that curare 

 in sufficient concentration accelerates the heart rhythm of Octopus 

 and Helix. According to Yung (1881), curare has sometimes a 

 depressor and sometimes a stimulating action on the heart of lameUi- 

 branchs. Plateau (1880) states that curare has a depressor action 

 on the crustacean heart, and according to Dogiel (1877) the drug has 

 no action whatever on the heart of the Corethra larva. 



Nicotine accelerates the heart rhythm both in crustaceans and in 

 molluscs (Yung, 1881, Plateau, 1880). 



Plateau states that atropine has a depressor action on the crustacean 

 heart. Yung and Ransom found that it acts as a stimulant on the 

 moUuscan heart. Dogiel states that atropine of sufficient concentra- 

 tion to affect the heart of the Corethra larva at all has a depressor 

 action. For an account of the action of these alkaloids on the tunicate 

 heart the reader is referred to the papers by Schultz (1901) and Hunter 

 (1903) . My own work does not include the heart of tunicates. 



In order to study the action of these drugs on the heart it is, in the 

 first place, necessary to sever the connection of the heart with the 

 central nervous system. All the animals worked on are provided 

 either with inhibitory or accelerator cardiac nerves or both (Carlson, 

 1909). The action of the alkaloids on the heart when introduced 

 into the intact animal is therefore complicated by their action on the 

 central ganglia or brain and on the peripheral ganglia other than those 

 in the heart. Satisfactory results can for that reason be obtained only 

 on the denervated or excised heart. The solutions of the alkaloids 

 may be applied to the surface of the excised heart and empty heart, 



