1918] Bovard: Nervous Impulses in the Earthworm 119 



When the length of the free nerve contained four ganglia, transmission 

 was easily demonstrated. 



In those eases where the dissection included the removal of the 

 dorsal wall, intestine, and the transection of lateral nerves, the trans- 

 mission easily ran for more than ten segments, but never for more 

 than twenty-eight. 



It has been demonstrated by Biedermann (1904) and confirmed by 

 my own experiments, that the impulses run long distances in the cord 

 when the worms are anesthetized in the middle region which is after- 

 wards treated with six per cent nitric acid. In such cases, records of 

 transmission were obtained when twenty segments intervened between 

 the still active anterior and posterior ends. Failures came more often 

 as the length of this etherized part was increased. One record was 

 obtained with the large Helodrilus where coordinationed movements 

 appeared in the posterior part when twenty-eight segments were 

 etherized and their muscles killed with nitric acid. 



These results fall somewhat short of the cases reported by Bieder- 

 mann, where coordinated movements were obtained through anes- 

 thetized parts two to three centimeters long, but the number of seg- 

 ments is not stated. The greater part of my records were obtained on 

 Helodrilus, where twenty segments of the body, in the part measured, 

 approximated two centimeters. While this does not show a great dis- 

 crepancy, my results are apparently nearer the lower figure quoted by 

 Biedermann. 



We can establish, then, no absolute limits, except to say that trans- 

 mission is fairly well accomplished over ten segments, may run to 

 twenty and even to twenty-eight, but that the longer the nervous 

 bridge the greater the difficulty. No records have been obtained where 

 thirty segments were concerned. 



One factor which makes the determination of any such records 

 very difficult is that impulses from normal stimuli in normal worms 

 starting down the length of the worm do not necessarily continue to 

 the end. The dying out of an impulse is quite a usual phenomenon 

 seen in the contraction waves that run only part way down the animal. 

 One of these impulses may start into the cord of the etherized part 

 and never reach the other end of the etherized part of the worm. This 

 does not mean that no impulses can come through, and so no limit can 

 be determined by this failure, but it does indicate a dying out of this 

 particular impulse somewhere in transit. Therefore, in the experi- 

 mental determination of the limits to transmission, as long as impulses 



