The hearing and counting of the fetal heart beat is the most important criterion of the condition of the baby in utero. This has been accomplished by various means as the science of obstetrics has developed. The tones were first heard by Mayor1in 1818 with the unaided ear. With the development of the stethoscope, various forms of these instruments have been used. The ordinary forms of the stethoscope have the disadvantage that they are not easily used by an operator when scrubbed up for a delivery. This disadvantage has been overcome by the head stethoscope, which can be used by the operator without manipulation by the hands. The disadvantage of this instrument, however, is that it is tiresome to the head and ears when worn for some time, and it interferes somewhat with the hearing of the operator for other sounds in the room. Furthermore, considerable practice is