_Its application to Medicine and Surgery._--The extreme sensitiveness of the microphone suggested its use for the observation of sounds produced within the human body, so that it might serve as a stethoscope for listening to the action of the lungs and heart. Dr. Richardson and Mr. Hughes are now busy in the attempt to carry out this idea, but so far the result is not very satisfactory, although they still hope to succeed. Meanwhile, M. Ducretet has made a very sensitive stethoscopic microphone, which we represent in fig. 51. It consists of a carbon microphone C P, with a simple contact, of which the lower carbon P is fitted to one of M. Marais’ tambourines with a vibrating membrane T. This tambourine is connected with another T′, by a caoutchouc tube, which is to be applied to the different parts of the body which demand auscultation, and which is therefore termed the _tambour explorateur_. The sensitiveness of the instrument is regulated by means of a counterpoise P O, which is screwed upon the arm of a bent lever, and to this the second carbon C is fixed. The extreme sensitiveness of M. Marais’ tambourines in transmitting vibrations is well known, and since their sensitiveness is further increased by the microphone, the instrument becomes almost too impressionable, since it reveals all sorts of sounds, which it is difficult to distinguish from each other. Such an instrument can only be of use when entrusted to experienced hands, and a special education of the organ of hearing is needful, in order to turn it to account. [Illustration: FIG. 51.] In a work lately published by M. Giboux on the application of the microphone to medicine, this stethoscopic system is rather severely criticised, and not without reason if, as M. Giboux asserts, it is only sensitive to the movements which take place on the surface of the body, and those which are internal are either lost or altogether changed in character. But without pronouncing on the improvements which may ultimately be made in the instrument, M. Giboux thinks that its most important use in medical practice consists in its allowing a certain number of students to observe with the professor the different sounds of the body, to study them with him in their different phases, and thus to profit more readily by his teaching. A microphonic circuit might bifurcate between several telephones, so that each person might hear for himself what is heard by others.