482 



Dr. A. D. Waller. 



To obtain the effects of indirect excitation two kinds of nerve-skin 

 preparation were used — (1) That of Roeber* and of Engelmannj 

 consisting of the sciatic nerve, knee, and skin of leg; (2) that of 

 Hermann, % consisting of spinal column and skin of back. 



In the case of indirect excitation, the response was observed during 

 and after excitation. In the case of direct excitation, the accidental 

 skin-current was exactly compensated, and the skin was excited while 

 the galvanometer was short-circuited ; the galvanometer was put into 

 circuit between 1 and 2 seconds after excitation. 



Results. — 1. The normal current is negative (ingoing). It regu- 

 larly increases during the first 15 to 30 minutes after the skin is 

 put upon the electrodes. The ordinary value of its E.M.F. is from 

 0-01 to 0-10 volt, e.g.— 



m . Yoltagre of 

 Time. ° , 



current. 



Omin. -0-0010 



10 „ - -0080 



20 „ - -0265 



30 „ - 0-0330 



A lively skin gives greater current than a poor skin. Nevertheless, 

 the former may, at the outset, exhibit a small current by reason of a 

 positive (outgoing) effect due to manipulation. The latter gradually 

 subsides, and negative current therefore gradually augments. 



2. The normal response to direct excitation is positive (outgoing). 

 The excitation may be mechanical or electrical, by a condenser dis- 

 charge or by an induction shock, in a positive or in a negative 

 direction. 



The response is greater and smaller with stronger and weaker exci- 

 tation. The initial positive frequently gives place to a subsequent 

 negative phase, or a positive interrupted by a negative phase may be 

 witnessed. In such cases comparatively weak excitations were used. 

 With strong excitation the positive response is very persistent, and 

 there is a marked " deflection-remainder." 



The positive response to negative excitation generally exceeds the 

 positive response to positive excitation. 



Tetanising currents of alternated direction give positive response. 



The response to a single break shock exceeds that to the corre- 

 sponding make shock with the ordinary arrangement of an induction 

 coil. 



The response exhibits the phenomena of summation and of fatigue. 

 It is abolished at temperatures above +45° or below - 6° and by 

 mercuric chloride. 



* Roeber, « Du Bois-Reyinond's Archiv,' p. 635. 1869. 

 f Engeimann, ' Pfliiger's Archiv,' vol. 6, p. 127. 1872. 

 X Hermann, 1 Pfliiger's Archiv,' vol. 17, p. 292. 1878. 



