J. F. GASKELL 81 



vious paper." It was found that a small branch of the anterior 

 nerve could be traced directly to the wall of the lateral vessel in each 

 segment, and that this nerve was formed of processes of cells situated 

 in the central segmental ganglion. A branch of the posterior nerve 

 also appeared to run to the same vessel, though its complete conti- 

 nuity was not established. The vascular muscles are therefore in- 

 nervated by processes of cells situated in the central gangUon, the 

 arrangement being a segmental one. 



The lateral vessels were found to have a contractile rhythm with 

 an average beat of about six to eight contractions per minute, and this 

 rhythm was independent of nervous control, for it continued for many 

 hours after complete section of all the lateral nerves. Rhythmical 

 contraction is, in the vessels of the leech, the property of the vascular 

 muscle itself; that is to say, the beat is myogenic not neurogenic. 



The effect of section and stimulation of the lateral nerves upon the 

 contractile rhythm of the lateral vessels was also investigated. The 

 study of the vascular beat was much facihtated by the use of curare, 

 which completely paralyzes the longitudinal and circular muscles but 

 does not affect the vascular muscles. The dose required is large, 

 being about 0.2 cc. of a 1 per cent solution, but the differentiation of 

 the two types of muscle by the action of curare is a complete one. 

 Attempts were made to obtain some mechanical method of recording 

 the vascular beat but nothing sufficiently dehcate could be devised. 

 The beats were therefore observed under a dissecting microscope and 

 recorded by a key signal on a revolving drum. As the animal had 

 to be kept in Ringer's solution throughout the experiments, stimu- 

 lation was brought about by means of Lucas'^^ electrode appHed to 

 the main nerve chain, the only nerve left intact being the one it was 

 desired to stimulate. It was found that section of the anterior nerve 

 with the posterior nerve intact always caused definite slowing of the 

 rate of beat, while stimulation of this nerve with the posterior nerve 

 divided caused acceleration. The anterior nerve thus contains ac- 

 celerator fibers to the vascular muscle. Section of the posterior nerve 

 with the anterior nerve intact caused quickening of the rate, while 

 stimulation of this nerve with the anterior nerve divided in the cura- 



^^hucaSfK., J. Physiol., 1913, xlvi, p. xxxii. 



