INDUCED ELECTRICITY. 17 



gradually produced. The exciters were applied daily to the paralyzed 

 muscles without inconvenience, although the apparatus was of considerable 

 power. The sight was never in any way affected; and the patient never 

 perceived any luminous appearance during the operation. One day, the 

 inventor of a new galvanic apparatus applied to me to make trial of his 

 machine. Not being then aware of any facts that shewed the necessity for 

 caution, I directed the current of this machine, at its weakest, upon the 

 paralysed muscles, which contracted, but much less strongly than they 

 ordinarily did under the use of the induction apparatus. At the same 

 moment the patient saw a considerable light in the eye of the corresponding 

 side. He called out, "Your room seems all on fire!" He begged of me 

 that I would desist from making the application. On recovering from the 

 dazzling he complained of much obscuration of the sight ; and could not see 

 towards the side on which the galvanism had been applied. The other eye 

 did not suffer. I ordered him an immediate footbath, and a blood-letting on 

 his return home. The sight did not improve ; and, notwithstanding the use 

 of various stimulants and of an appropriate treatment, only very slight 

 amendment was obtained. 



It is to this accident that I owe the discovery of an action of 

 galvanism on the retina, far more powerful than that of induced 

 electricity : a discovery which led me, in its turn, to researches 

 into the different properties of the various kinds of electricity 

 with regard to the production of phosphenes. 



This unfortunate circumstance, not possible to have been fore- 

 seen, ought not to be lost to science. It furnishes therapeutic 

 applications that are of great importance to the sick ; shewing that 

 induced electricity, furnished by an electro-dynamic apparatus 

 even of great power, has no sensible action upon the retina, wliile 

 galvanism, even in a very feeble dose, energetically influences that 

 organ. It is therefore legitimate to hope that the judicious 

 employment of the electricity of contact may produce therapeutic 

 effects that will be useful in the purely nervous affections of the 

 eye. Such expectations have been confirmed by experience. 



To sum up — 1. Galvanic electricity acts strongly upon the 

 retina, when the excitation is directed upon parts in which the 

 fifth nerve ramifies. 2. This kind of electricity may be an useful 

 therapeutic agent in purely dynamic affections of the sight. 3. 

 On the contrary, induced electricity, yielded by an electro-dynamic 

 apparatus, acts very feebly upon the retina. 4. But, for the 

 reason that induced electricity is insufficient when it is necessary 

 to stimulate the retina, it is exclusively adapted for the cases in 

 which it is wished to stimulate the facial muscles, without exposing 

 the retina itself to the perils of over-stimulation. 



Part III. 



INDUCED ELECTRICITY. 



Although it forms no part of my present plan to explain the 

 principles that govern the development of induced currents (prin- 



c 



