A. J. CARLSON 565 



done without the least injury to the lateral nerves. This makes an 

 ideal preparation. It is a simple matter to apply a solution to the 

 first two segments and absolutely prevent it from getting to the hind 

 portion of the heart and, conversely, to bathe the nerve cord on the 

 posterior end of the heart in a solution without the solution reaching 

 to the first two segments. Any change in the rhythm of the first two 

 segments on application of a drug to the nerve cord of the posterior 

 end of this heart preparation can be due only to a change in the ac- 

 tivity of the ganglion cells which maintain the rhythm. And again, 

 the change in the rhythm of the first two segments produced by a solu- 

 tion appHed to these segments alone is evidently not an action on 

 ganglion cells but must be an action on the nerves and nerve endings 

 in the muscle or on the muscle itself if we assume that local reflexes 

 play no role. For accurate determinations of the changes in the 

 rhythm in the two anterior segments in this preparation, the graphic 

 method was always used. 



On this preparation an extended series of tests of the principal alka- 

 loids were made, the results yielding the conclusion expressed above. 

 All the alkaloids tested act on the nerve cord. Some of them, espe- 

 cially veratrin, digitalin, and nicotine act also on the muscle, and it is 

 probable that all of them act on the muscle if in very strong solution ; 

 but their action on the nerve cord or ganglion cells is much more rapid 

 and intense, and all the alkaloids, moreover, act on the nerve cord in 

 a dilution which has no or at least a very slight and gradual action on 

 the muscle. Thus a solution of 1 per cent curare or atropine in plasma 

 or sea water stimulates the nerve cord powerfully at the very instant 

 of application, while no change in the rhythm follows its application 

 to the muscle. Further work in this line will probably show that 

 dift'erence in the action of the alkaloids on the nervous and on the mus- 

 cular tissues in the heart is only one of degree, the ganglion cells 

 being more permeable to the drugs and the muscle cells ha\dng lower 

 excitability. 



The action of these alkaloids (curare, atropine, and nicotine) 

 on the whole heart of crustaceans and the molluscs is in all essentials 

 the same as their action on the nerve cord or ganglion cells in the 

 Limiilus heart. The conclusion seems obvious that their action on 

 the crustacean and molluscan heart is also primarily on the ganglion 

 cells. 



