ON THE MAMMALIAN NERVOUS SYSTEM. 293 



Just as the mechanical stimulus affords, perhaps, the best control of the electrical 

 stimulation of fibres, so the chemical, since it excites centres powerfully, affords a 

 means of producing electrical changes in the efferent fibres from such centres which 

 cannot possibly be due to actual escape of the exciting current. 



For the performance of this method we have prepared the cord or nerve for 

 connection with the non-polarisable electrodes as described previously, and then 

 exposed for a short distance the external jugular vein, applying a small clip to the 

 latter. 



Two minims of the essence of absinthe were then injected with a hypodermic 

 syringe inserted through the vein wall into the freely flowing blood stream. 



The animal was then carefully observed and the first twitching indicating the 

 commencement of a cortical discharge noted. It coincided in time with the beginning 

 of large electrical effects as evidenced in the galvanometer. For further facts relating 

 to this method we would direct attention to the Chapter dealing specially with the 

 results thus obtained, vide p. 511. 



3. Extra Apparatus. 



The apparatus used for investigating the muscular changes evoked by excitation of 

 the central nervous system was either adapted for a direct record of the character of 

 the muscular contraction or for ascertaining the moment of its commencement. 



When necessary the muscular contractions, whether evoked by cortical or spinal 

 excitation, were recorded by means of a spring lever, made on the pattern of that 

 employed by FICK. for obtaining isometric muscular effects. The muscle was attached 

 so that any changes in its tension were communicated to the spring, the small move- 

 ments of which were magnified fifty times by a lever attached to its end. The lever 

 recorded its movements on the blackened paper of an ordinary drum driven regularly 

 by a clock. 



When it was desired to ascertain the moment of the commencement of the 

 muscular contraction, however evoked, the method employed by TIGERSTEDT was used. 

 The Mammalian muscle was attached to the light " unterbrecher," which carried a 

 weight of 10 grm. placed upon its axle, to ensure a steady pull upon the large muscle 

 and a proper tension of its attachment. The unterbrecher, as in TIGERSTEDT'S method , 

 formed a key in a separate circuit, which included a battery of three Grove's cells and 

 one of SMITH'S* new electromagnetic signals. The break of the key and the consequent 

 movement of the signal was recorded upon the glass plate of a spring myograph 

 (DU BOIS-REYMOND'S Federmyoyraphion) which travelled at a rate of 2 centims. in 

 second. 



* ' Philosophical Magazine,' 1889. 



