AFTER ELECTRICAL STIMULATION. 271 



out, is not to be doubted, for the contractions of the animal's limbs can 

 be only very incompletely arrested by ligature of the nerve in the middle 

 of the intermediate tract ; for this ligature to be efficient it must be 

 applied immediately above the entrance of the nerve into the muscle. 

 With regard to the action of this outflowing- of tension electricity 

 on the needle of the multiplier we need have no anxiety.' 



It only need be added to this remark, that even with the best pos- 

 sible insulation, unipolar action is not excluded under the above circum- 

 stances, if only the conditions already mentioned are favourable to it. 



In vol. ii. p. 5!) du Bois-Reymond shows proof that the negative 

 variation of the muscle-current cannot depend on the invasion of the 

 circuit of the multiplier by inductive electricity. For this purpose 

 it is only necessary to ligature the nerve of the gastrocnemius 

 between the stimulated tract and the galvanometer tract, in order 

 to see the needle remain motionless in its place, the muscle also 

 remaining at rest. ' Care must be taken ' in using an induction 

 apparatus of any kind for tetanising, as du Bois-Reymond observes, 

 * that the ligature be placed close to the point where the nerve 

 enters the muscle. The ground for this rule lies in unipolar 

 induction-contractions. And if it be not adhered to, the muscle does 

 not remain at rest, as above described, in spite of the most careful and 

 secure ligature of the nerve; and simultaneously with the slight 

 tetanus which is still produced, there occurs a correspondingly small 

 action on the needle.' 



Du Bois-Reymond expresses himself in a precisely similar manner 

 when dealing with the negative variation of the nerve current. 



Ligature and section,' he says, ' here also prevent all trace of 

 movement of the needle. In these experiments one must not use the 

 induction apparatus for tetanising, on account of unipolar actions, but 

 must employ instead a battery, the current of which is broken and 

 reversed at the same time by means of a PoggendorfF " inversor." ' 



In the section which treats of the influence of various circum- 

 stances on the amount of negative variation when tetanising with 

 reversed currents, du Bois-Reymond says (vol. ii. p. 449), ' Further, 

 it is not unfrequently necessary to exchange the induction apparatus 

 for Poggendorff's inversor. This is the case in the first place when 

 the amount of negative variation in tetanisation is to be compared 

 with the amount of the negative phase of the electrotonic state, 

 which is itself produced by a current of equal strength with the 



tetanising current In the second place, this necessity arises 



when one is apprehensive of disturbances of the result consequent 



