The Ulster Medical Society

ear attaclhnment may be conniected to the receiver by means of rubber tubing, so that the physician can listen to heart-sounds in the familiar manner. 'I'he microphone,. which takes the form of a vibration pickup, is extremely unresponsive to extraneous souLIds, andl a rubber ring surrounding it reduces to a minimum noises which mav be caused bv handlinig the instrument. 'T'he frequency response ranges from 60 to 1,500 cycles per second, amply covering the band encountered in listening to heart-sounds. An important feature of the 3AStethoscope is its filter circuit, which isolates and accenituates murmur-sounds, so significant and yet so difficult to detect with an ordlinary acoustical stethoscope. 'T'his filter circuit in the amplifier diminishes the response at both the low and high frequencies, and can be included or omitted at will by the turn of a switch. 'I'hus the intensity of normal heart-sounds is lowered andl the loudness of any murmur-sounds which may be present is accentuated. Consultations are facilitated by provision for an additional receiver, an extremely valuLable feature enabling two phvsicians to listen simultaneously to a patient's heart-sounds from the same body location. 'The amplifier has a maximum gain of sixty decibels, and is sufficiently powerful to operate the additional receiver. Volume is controlled by a potentiometer situated on the patnel. The 3A1Electrical Stethoscope is completely contained in a small fabrikoid case, similar in size to a doctor's instrumllenit bag. It measures 12! inches in length, 83 inches in height, and 43 inlches in depth, anid weighs only fourteell poundls. Operation of the instrument is extremely simple. 'I'he physiciannmerely attaches the tube of his acoustical stethoscope to the receiver, clips the receiver to his coat, and turns the volume control until he obtains the desired loudness. 'rhe microphone is then lightly pressed against the patient's body in the same manner as when using a conventional stethoscope. \When wislhing to cliagnose murmur-sounds, the knob marked "filter" is turned to its "in" position. Low-tension supply for the valve filaments is dIrawn from 1.5 unlit cells of the flashlamp type, and the anodes are fed from a 4.5-v-olt miniature dry battery, the whole issue being neatly housed in the lower part of the case. 'I'hese batteries are of the new plug type, which makes replacement simple and easy. 'T'hey may be purchased anywhere. Further particulars may be obtained from WN'estern Electric Company Limited, Bush House, Aldwych, London, NNT.C.2; telephone: T'emple Bar 1001.