REQUISITES FOR ELECTRO-MEDICAL INSTRUMENTS. 235 



11. Indications and Contra-indications for Eapid 

 Intermissions. 



A knowledge of the foregoing facts enables us to foresee the 

 numerous indications or contra-indications for rapid intermission 

 of the currents ; and I proceed to set forth what a long and daily- 

 experience has taught me upon this subject. 



A. — Cases in ivJiich the emfloijmeni of rapid intermissions is in- 

 dicated. — (a). The property possessed by rapid intermissions, of 

 producing artificial contractions which perfectly imitate voluntary- 

 movements, enables us to employ them in the study of the indivi- 

 dual actions of muscles. But it will be seen that such researches 

 require the employment of an intermittent current of extreme 

 rapidity, especially for the muscles of the face. The magneto- 

 electric instruments, the intermissions of which are scarcely of 

 sufficient rapidity to produce contractions without tremor of the 

 muscles of the limbs and of the trunk, have been insufficient for 

 my researches upon those of the face. The constant quivering of 

 the facial muscles, when excited by the currents from such instru- 

 ments, forbid one to observe exactly the individual influence of 

 each one upon expression. 



(&). The study of the physiological action of slow and of rapid 

 intermissions has shown that we can, by the aid of the former, 

 act with more or less energy upon the contractility or the sensi- 

 bility of muscle. For, since every electric excitation of a muscle 

 necessarily produces at once a sensation and a contraction, we 

 may diminish at pleasure the force of the contraction, and may 

 increase the sensation, by combinining the current of the primary 

 coil, the special action of which upon muscular sensibility is known, 

 with rapid intermissions, or vice versa. 



The power of energetically arousing the muscular sensibility by 

 the aid of rapid intermissions finds its most useful applications in 

 cases in which the muscles have lost their sensibility. Such cases, 

 as I shall have occasion to show, are not infrequent ; and I shall 

 hereafter, cite numerous examples. 



I have often found muscles which, whether deprived or not of 

 the power of voluntary movement, were completely insensitive to 

 the electric excitation ; so that I was able to produce very ener- 

 getic contractions by the application of the most rapid currents, 

 without the patients being conscious of them. The skin covering 

 such muscles was also in some cases insensitive ; but in others it 

 retained its normal sensibility. 



Patients who are deprived only of the sensibility of the skin 

 (antesthesia or analgesia) preserve their consciousness of the move- 



