256 ON POSITIVE VARIATION OP THE NERVE CURRENT 



Unpolarisable electrodes were almost exclusively employed. The 

 lower ends of these were filled with saline clay, into which was intro- 

 duced a brush steeped in -6 per cent, salt solution. An ordinary 

 camel-hair pencil was used, and this was cut off about I cm. above 

 the lower end of the quill. If there are several such brushes at hand, 

 it is easy to find one to suit any electrode tube, fitting- firmly into 

 it. These electrodes are made like the pencil electrodes of Fleischl, 

 with this difference, that modelling clay serves instead of gypsum 

 to close the lower extremity. This material is easily renewed after 

 each experiment. These electrodes are only occasionally completely 

 free from current. I therefore measured this current, before each 

 experiment, by bringing the two points into direct contact. Its 

 strength is given in each case in the experiments hereafter quoted. 

 As we are dealing with nerve currents, the galvanometer used was 

 very sensitive. Consequently the electrode deflection was sometimes 

 considerable ; but it must not be forgotten, however, that after intro- 

 duction of the nerve with its great resistance into the circuit, the 

 current of the electrodes has not nearly so marked an effect on the 

 deflection of the needle caused by the nerve current, as it would have 

 had without that increase of resistance. On the amount of negative 

 or positive variation observed after compensation of the nerve current, 

 the current of the electrodes has no influence ; I therefore took no 

 further pains to secure perfectly unpolarised electrodes, although these 

 are indispensable in other cases. If a larger number of electrodes be 

 prepared on the type above described, two may generally be found 

 which are quite, or nearly devoid of current at least for a time. 

 The stimulating currents were also introduced by these electrodes. 

 A moist chamber protected the nerve from drying, but unavoidably 

 favoured unipolar action. Very weak stimulating currents were 

 therefore used and numerous control experiments were made, 

 especially those in which the nerve was crushed in the inter- 

 mediate tract. The secondary coil (5000 turns) of the induction 

 apparatus (worked by I Daniell) was scarcely ever brought nearer 

 than 20 cm. to the primary, under which condition unipolar action 

 was not noticeable. In spite of the resistance of the electrodes, the 

 induction current thus obtained proved quite sufficient. On account 

 of the many drawbacks to the ordinary induction apparatus in use 

 in physiological laboratories, the following method was employed to 

 produce induction currents. 



In order to obtain reversed but physiologically equal currents, a 

 few years ago I improvised the following apparatus. A secondary 



