l^N DENTAL OPERATIONS. 81 



Without discussing the various opinions which 

 have been broached upon the subject, or attempt- 

 ing here to offer a rationale of elpctro-anassthetic 

 action, it will be sufficient to take up at once the 

 practical matters connected with it, the action of 

 the instruments employed, and the most effica- 

 cious mode of applying them. 



Hitherto, the greatest amount of success has 

 attended the use of the instrument called the 

 galvanic coil machine, in one or other of its 

 forms. The action of this instrument depends 

 upon the repetition of a great number of ver}^ 

 minute shocks, in such rapid succession as to 

 approximate the character of a continuous cur- 

 rent. These shocks, although individually very 

 feeble, give rise to accumulated sensations, which 

 increase in power, generally in proportion to the 

 rapidity with which they succeed each other, the 

 total effect being of course also modified by the 

 absolute strength of each individual shock. The 

 force of the single shock depends, first, upon the 

 quantity of wire contained in the secondary coil ; 

 secondly, upon the amount of magnetism in the 

 iron core, inducing upon the secondary coil ; and 

 this magnetism again depends upon the relation 

 which the primary coil and battery bear to each 

 other. As there is no standard assumed for the 

 construction of these instruments, each manufac- 

 turer follows his own inclinations, often without 

 being guided by any definite electrical laws : hence 



