1918] 



Bovard: Nervous Impulses in the Earthworm 



123 



reinforced by outside reflexes ; and so, unless special methods are used, 

 the reactions of these short fiber systems would not be observed. 



A frequent observation on the locomotor habits of worms is that 

 the wave of contraction runs for a short distance and then disappears. 

 This was a source of great inconvenience in determining the rate of 

 impulse down the cord. A method was devised whereby electric con- 

 tacts were successively made as the wave of contraction passed along 

 the worm. These were recorded on a drum from which measurements 

 were easily made and speeds computed (fig. 12). 



ant 



x. c.pl 



Fig. 12. The apparatus for measuring the speed of nervous impulses through 

 the nerve cord in an anesthetized region was as follows: a.l. and p.l. are levers 

 pivoted at piv. The lower part of the lever n is a sharp, very fine needle. One 

 of these is thrust into the muscles of the first segment in front of the anesthet- 

 ized part m. and the other into the muscles just behind this region m. The 

 upper ends of these levers is quite long so that very slight movements of the 

 lower part will produce considerable movement in the upper part. Platinum 

 contacts were provided at pt.c. and each lever was connected by battery to 

 signal magnets, a.s. and p.s., which gave a record on a smoked drum of a 

 kymograph. When the locomotor movement of the anterior part of the worm 

 had reached the muscles at x. the electrical contact would be made in lever a.l., 

 which registered on a fast revolving drum at a.s. Now when the nervous impulses 

 had passed through the anesthetized area m. and reached the muscle y. another 

 electrical contact was made by lever p.l. and registered by signal magnet p.s. 

 The speed of the drum being measured, the speed of the impulse could be 

 calculated. 



