HISTORY, &c., OF INDUCTION INSTRUMENTS. 309 



that he has adapted the double induction. It is to be regretted 

 that the Paris hospitals are supplied only with the first or small 

 model, which is insuificieut, not only on account of the weakness of 

 its current, but also from the absence of the current of the second 

 coil. 



MM. Breton freres have manufactured a large and a small 

 magneto-electric instrument. According to M. Le Eoux, they have 

 endeavoured to add the double induction to the former. 



I have had occasion to examine the differential action of the 

 two coils in one of two of these instruments which I found in one 

 of the Paris hospital^!, and, to my great surprise, the distinctive 

 characters of their differential action were scarcely appreciable. 



What could be the reason of this ? Have MM. Breton observed 

 those proportions of length and diameter, which the wires of the 

 first and second coils should possess, with regard to the initial 

 force of the magnet, in order that double induction may be pro- 

 duced ? Are the two coils perfectly independent of each other ? 

 Not having unw'ound them, I am unable to explain the actual 

 reason. It would be easy for these skilful manufacturers, who, 

 by having been the first to construct portable magneto-electric 

 instruments, have so much contributed to popularize the applica- 

 tion of induction currents, to fulfil the desideratum which it has 

 been my duty to point out. 



B. — Slotv or raj^id intermissions. — In the part (Chap. I., Part 

 I.) in which I have described the properties and the particular 

 arrangements which every induction instrument intended for 

 medical practice should possess, I have made known the special 

 action which slow or rapid intermissions exert, — 1, upon electro- 

 muscular contractility ; 2, upon muscular sensibility ; 3, upon 

 muscular tonicity ; 4, upon muscular nutrition ; 5, upon electrv 

 cutaneous sensibility. 



Lastly, I have passed in review the chief pathological conditions 

 in which rapid intermissions should be preferred ; and also those in 

 which they are formally!; contra-indicated, and in which they 

 should be replaced by intermissions more or less distant, on pain 

 of sometimes occasioning accidents. It follows that any magneto- 

 electric apparatus which is not so constructed as to yield currents 

 with slow or rapid intermissions, according to the therapeutic in- 

 dications to be fulfilled, will be inapplicable in a great number of 

 cases. 



This has been well understood by M. Gaiffe, who, in imitation 

 of my magneto-electric instrument, allows the electrodes to receive 

 only one or two intermissions for each revolution of' the large 

 wheel. 



