434 ELECTRO-PHYSIOLOGY CHAP. 



This nerve, together with the sinus, can be completely isolated 

 from the remainder of the heart, when it forms the sole channel 

 of communication to the auricle which, with the ventricle, is 

 separated from the sinus. After the separation has been made, 

 both auricle and ventricle remain completely quiescent, and only 

 resume pulsation later, so that the experiments can be effected 

 during the quiescent period. To this end the apex of the 

 auricle is burned, yielding in consequence a strong de- 

 marcation current, when the leading-off electrodes are in contact 

 with the thermic section and the uninjured base. Like the 

 ventricle current, this auricle current declines rapidly at first, 

 then more slowly. During this time each vagus excitation gives 

 rise to a positive variation, which begins quickly, reaches a 

 maximum in about 10 sees., and at cessation of excitation 

 sinks with increasing rapidity, so that after 18 20 sees, the 

 magnet takes up the position which it would have occupied in 

 the absence of vagus excitation. There can be no doubt that 

 this effect depends upon changes that have arisen in the un- 

 injured part of the auricle, and are " accompanied by increased 

 positivity of that part, just as contraction of the auricle is 

 accompanied by diminished positivity of uninjured tissue." If 

 the auricle now recommences to beat, each contraction gives 

 rise to a negative variation of the demarcation current, far larger, 

 as a rule, than the positive variation ; cases, however, occur 

 in which both kinds of variation are about equal in magnitude 

 yet even here there is a very characteristic difference with regard 

 to rapidity of decline in the two effects. The swing back of the 

 magnet is far more rapid after a negative than after a positive 

 variation. If the excitation of the vagus is continued for any 

 length of time, the positive variation may subside completely, 

 even during the excitation. These galvanic effects of the vagus, 

 like its inhibitory function, are abolished by atropin poisoning. 



As is well known, the heart is influenced not only by in- 

 hibitory, but also by antagonistic, viz. excitatory, nerve-fibres, 

 which suggests the possibility of obtaining opposite galvanic 

 effects by excitation of the latter. And Gaskell, in fact, has 

 succeeded under given conditions in obtaining a negative varia- 

 tion of the quiescent ventricle (64). 



We ourselves performed experiments on the innervation of 

 the claw-muscles of the crab (65), the results of which will have 



