REQUISITES FOR ELECTRO-MEDICAL INSTRUMENTS. 233 



tial properties. It is evidently necessary that any other experi- 

 menter should place himself under the same conditions of ex- 

 periment, if he would judge correctly of the value of my electro- 

 physiological researches and of the deductions drawn from them, 

 or if he desires to apply them in practice. From this point of 

 view, at least, electro-medical instruments should be constructed 

 in the manner that I have laid down. 



§ II. The slotv or rapid intermissions of the electro-medioal instru- 

 ments ]3roduce sjpecial physiological effects, and cannot replace 

 one another in practice. 



In order to make clear the utility or the necessity, the incon- 

 veniences or the dangers, of faradic currents with intermissions 

 more or less slow or rapid, it is sufficient to describe the physio- 

 logical phenomena that are produced under their influence ; 

 and to frame from these, immediate practical deductions, which 

 'will be fully borne out by the facts stated in the course of this 

 volume. 



I. Action of the Eapid Intermissions of Querents. 



A. — Upon electro-muscular contractility. — A muscle, which re- 

 ceives the stimulus of a single intermission of an induced current, 

 contracts, but immediately falls back into complete relaxation. 

 If this intermission be followed by many others, sufficiently near 

 together, the muscular contractions follow one another; and the 

 muscle becomes less completely relaxed between the inter- 

 missions in proportion as they are less distant. It follows that 

 the muscular fibres contract more, the more rapid is the induced 

 current. 



It is necessary to guard against the supposition that a current 

 of rapid intermissions causes more energetic contraction of muscle 

 than a current of slow intermissions. That such a belief would 

 be erroneous may be shown by the following experiment. If we 

 apply a rapid and a slow current alternately to a paralysed muscle, 

 the irritability of which is undiminished, for example, to the 

 flexor communis digitorum, and if we attach a weight to the fingers 

 moved by the muscle, we shall see that the rapid current does not 

 give the muscle power to sustain a heavier weight than it would 

 sustain under the influence of the slow current. If, under a raj)id 

 current, the extent of the muscular contraction is increased, and 

 if therefore the movement of a finger is more extensive, this is 

 because, the fibres relaxing little or not at all during the brief 

 intervals, each excitation shortens them more and more. To 



