In order to meet the military requirements for a headset that could be worn under the MK-1 helmet, midget hearing aid receivers were redesigned for this application. Data is presented showing characteristics of the original design adopted and of subsequent improvements resulting in improved performance. Some of the methods for securing adequate performance in quantity production and methods for 100 percent inspection of frequency characteristics are described.

Adenocarcinoma of the prostate may occasionally mimic primary carcinoma of the rectum in both symptoms and gross character of the lesion. Establishment of the proper diagnosis is important because of the wide difference in treatment and prognosis. Since both tumors are adenocarcinomas, the biopsy specimen may be equivocal if the lesion is anaplastic, and the diagnosis may depend upon the history, metastatic picture, serum acid phosphatase, and response to estrogen therapy. Prostatic origin should be considered in rectal lesions, if the prostate gland is not palpably definable, separate from the mass.

The experience gained in fitting a large number of impaired persons with hearing aids is presented, showing illustrative ranges of impairment between 30 and 100 decibels fitted with three progressively-powered hearing aids. General features of such hearing aids are discussed, showing circuits and arrangements for peak clipping and automatic gain control. The microphone and air and bone receivers are described, considering features developed for providing optimum reliability in service such as moisture proofing, and design arrangements providing miniaturization concomitant with ruggedness.

An artificial mastoid for testing bone conduction receivers is described. It consists essentially of a stiff metal bar which has a fundamental resonant frequency above the measurement range, with a strain-sensitive translating element fastened to the under side and a compliant pad on top. The translating element is a slab of activated ceramic, which is essentially invariant to humidity and temperature changes. The compliant pad generally used is Koroseal No. 74, which simulates the flesh over the mastoid prominence reasonably well. Koroseal No. 15 simulates flesh better but is less rugged. Calibration methods are discussed.

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