310 LOCALIZED ELECTRIZATION. 



It is to be hoped that all other manuracturers will follow an 

 example that is easy of imitation. It would be a great step in 

 advance. 



C. — Graduation. — Every medical induction instrument should 

 afford a means of distributing its currents in doses proportionate 

 to the very different degrees of excitability (which may depend 

 upon the state of health or upon the state of the disease) of the 

 sensitive or motor nerves, of the muscles, and of other organs more 

 or less deeply situated (see § IV., p. 241). Moreover, the gradua- 

 tion should be exact, and should range over a sufficiently extended 

 scale. 



Without these conditions, magneto-electric instruments are often 

 inapplicable to medical practice. 



The instruments of Pixii, of Clarke, and of Saxton are entirely 

 AAithout graduation. Page was the first who endeavoured to obtain 

 it, by rendering the magnet of his apparatus movable (see fig. 75), 

 so that it could be placed nearer to or farther from the soft iron. 

 The idea rested upon the principle, that, in a magneto-electric 

 instrument, the farther the magnet is moved from its soft iron or 

 its electro-magnet, the more the inductive influence of the alternate 

 changes of state of these magnets will be weakened, and vice 

 versa. 



Since then, this method of graduation has been imitated by most 

 makers. But it is very defective, because there is no proportion 

 between the divisions of the graduator and the diminution or 

 augmentation of the intensity of the current, when the magnet 

 is moved farther from or nearer to the soft iron. 



The graduator is, in general, a small metallic stem, which serves 

 to draw back or to push forward the magnet. It is about a centi- 

 metre and a half in length ; and its action only becomes sensible 

 in its second half, because, in the first half, the soft iron does not 

 exert on the magnet any physiological influence that is appreciable 

 in man. From the commencement of the second half, or there- 

 abouts, of the graduator, the current increases in enormous pro- 

 portion (in geometric ratio, or nearly as the square of the distance). 

 It is impossible exactly to apportion the power of faradization by 

 means of a system that is so irregular. 



Moreover, even if the movement of the graduator and the increase 

 of the force of the current were in exact relation, or, in other words, 

 if the increase and diminution of the intensity of the current were 

 in aritlimetical proportion to the movement, the system would still 

 be inapplicable to localized faradization, either for physiological, 

 pathological, or therapeutical purposes, because it is not made 

 upon a scale of sufficient extent. 



