November 18, 1904.] 



SCIENCE. 



685 



cells even in the vertebrate heart. This must 

 necessarily lead to a revision of some of our 

 views of the nature of the action of drugs 

 and certain solutions on the heart, as these 

 are based on the myogen theory of the heart- 

 beat. 



The preparation' of the Limulus heart for 

 the study of the action of solutions on the 

 ganglion cells apart from their effects on the 

 muscle is represented in Fig. 1. The gan- 

 glion or median nerve-cord is extirpated from 

 the first and second segments, the lateral 

 nerves being left intact. The removal of the 



segment the action of a solution applied to 

 the anterior end of the heart can not be due 

 to or complicated by the effects of this solu- 

 tion on the ganglion cells, care being taken, 

 of course, that the solution does not touch 

 the posterior end of the heart. But although 

 this possibility is excluded, the solution ap- 

 plied to the anterior end of the heart may 

 affect ■the rhythm of this part of the heart in 

 either o'r all of these three ways: (1) It may 

 act directly on the muscle, (2) it may act 

 on the motor nerves and nerve-endings, or 

 (3) it may act on sensory nerves and nerve- 



FiG. I. Heart of Limulus as prepared for studying the effects of solutions on the ganglion 

 cells apart from that on the muscle. Dorsal view. A, anterior arteries; LA, lateral arteries; 

 LN, lateral nerves; UNO, dorso-median nerve- cord or ganglion; OS, ostia; H, attachments for 

 graphic registration of the contractions of the ganglion-free segments. 



nerve-cord removes the ganglion cells from 

 that part of the heart. The extirpation of 

 the nerve-cord in the first two segments di- 

 minishes the strength of the contractions in 

 these segments, but it does not affect the 

 rate of the beats or the strength of the con- 

 tractions in the other parts of the heart. 

 After removal of the ganglion from the ante- 

 rior end of the heart the contraction of the 

 muscle in these segments is caused by im- 

 pulses from the ganglion cells situated in 

 the ' nerve-cord of the fourth, fifth and sixth 

 segments, these impulses passing forward to 

 the muscle in the lateral nerves. The heart- 

 muscle may now be removed for a distance 

 of one centimeter or more in the region of 

 the second pair of lateral arteries, leaving the 

 two ends of the heart connected by the lat- 

 eral nerves only. The anterior end of the 

 heart is supported and connected with a re- 

 cording-lever for graphic registration in the 

 manner indicated in Fig. 1. 



By the removal of the nerve-cord and 1,he 

 separation of the heart-muscle in the second 



endings, the impulses being carried to the 

 ganglion cells in the posterior part of the 

 heart by means of afferent fibers in the lat- 

 eral nerves. This would be a true reflex ac- 

 tion. I have positive proofs of the presence 

 of such a local reflex mechanism in the 

 Limulus heart. 



Conversely, if we apply the solution to the 

 posterior end of the heart, that is, to the 

 nerve-cord behind the lesion in the second 

 segment, taking care that none of the solu- 

 l!fon reaches the isolated anterior end, the 

 changes in the rhythm of the two anterior, or 

 reacting segments must be ascribed to 

 changes in the activity of the ganglion cells 

 due to the direct influence of the solution. 

 It is possible to remove the greater part of 

 the heart-muscle of the portion of the heart 

 including the fourth to the seventh segments, 

 leaving the nerve-cord, the lateral nerves and 

 their main connections intact, without greatly 

 disturbing the activity of the ganglion. The 

 effects of the solutions on this isolated gan- 

 glion do not differ essentially from the effects 



