318 LOCALIZED ELECTRIZATION. 



This, then, being established, it is more simple and prudent to 

 make a capillary opening through the caoutchouc covering, by 

 which the gas may escape if the pressure becomes too great, 



E. — Power and size of the electro-dynamic instruments. — In 

 certain cases, as 1 have said, the induction instruments should be 

 very powerful (see III., p. 239). We have here to consider their 

 physiological action, atid from this point of view to determine their 

 power. This, therefore, is not so simple a matter as was thought 

 by MM. Becquerel, M'hen they wrote :— " The extra current, and 

 the current of the first hind, do not ^possess an elective action over this 

 or that function, hut they have an action more or less energetic, by 

 reason of their tension." ... It was a mere matter of inex- 

 perience, at the time when M. Becquerel the younger maintained 

 this position in defence of a physical theory. It was no longer a 

 matter of inexperience alone, when it was maintained before the 

 Institute, eight years subsequently, by M. Becquerel the elder ; 

 because it would have been easy for him to have acquired a 

 personal knowledge of the subject, by submitting to my experi- 

 ments, as so many other physicists of equal position had done. 

 But, fortunately, he has been unable to arrest the progress of 

 science, and it is now perfectly established — 1. That the extra 

 current, which has very little tension, or infinitely less than the 

 induced current, excites acutely, and more acutely than the latter, 

 the sensibility of the greater number of the organs situated 

 beneath the skin (the nerves, the muscles, the bladder, the uterus, 

 the testes). 2. That its therapeutic application, in full dose, is 

 indicated in the cases where these organs are deprived of sensi- 

 bility, in cases where it is necessary to act upon the nutrition 

 (which I liave observed that it seems most to stimulate, perhaps 

 by producing less contraction of the capillary vessels than the 

 induced current). 3. That, by reason of the weakness of its 

 power to penetrate to deeper tissues (in other words, the weakness 

 of its tension), the extra current is the only one that is adapted 

 for cases in which it is indicated strongly to excite the contractility 

 and sensibility of superficial muscles, without acting upon those 

 that are beneath them. 4. That, in order to obtain this special 

 physiological action of the extra current, its wire should have a 

 certain diameter and a sufficient length, so as to have an initial 

 force proportionate to that of the magnet and of the battery. 5, 

 and lastly. That this extra current becomes powerless, when we 

 wish to penetrate a great thickness of tissue, so as to excite deeply- 

 situated organs, such as muscles of the deeper layer in very fat or 

 cedematous persons, or when we wish to excite very acutely the 

 sensibility of the skin, as in profound anaesthesia. It is then 



