Limitations of the cholecystogram.

There is a little doubt that the spontaneous passage of gallstones occurs sometimes without pain or jaundice. This is probably more frequent than is realised. While the cholecystogram is a reliable investigation and of great assistance to the clinician, occasionally a normal gallbladder will be demonstrated, when it has previously been the resting place of small gallstones. Four cases are described in which patients suffering clinically from cholelithiasis are shown to have a normal cholecystogram, but on repeat examinations gallstones are demonstrated in each case over intervals of one or two years. It is suggested that gallstones had been present in all these cases at the time of the initial symptoms, but could well have passed prior to the first examination.

Variations in bronchial movement.

Studies of bronchial movement in bronchi and bronchioles following routine bronchography are presented with the aid of a magnification technique. Wide variations of calibre were demonstrated on full inspiration and extreme expiration, most marked in the smaller bronchi. During coughing, maximal differences of width were noted in the larger airways, with little change in the smallest bronchi. In order to assess the changes, reference is made to previous records when, using a three-channel writing oscillograph, bronchial measurements, intra-oesophageal pressures and lung volumes were estimated. Critical examination of the borders of the bronchial walls revealed that they were never straight nor truly parallel. They had smooth, undulating outlines, which were seen to alter on serial films. Irregularities in the airways without disease can be considerable, but when destructive changes are present, gross deformities may become apparent. With a full inspiratory effort, bronchial walls may be completely extended and appear normal, but on radiographs taken on expiration weakness of the bronchial wall may be revealed which otherwise would be missed. The inclusion of routine expiratory films on all bronchographic examinations is recommended.

Measurements of the Baseband Frequency Response of a 1-km Fiber.

Typical light-emitting diodes have a spectral width between 300 A and 500 A. This is sufficient to cause significant pulse broadening as a result of material dispersion in a long optical glass fiber. An experiment was performed to measure the magnitude of this effect in a fiber of 1-km length. The experiment measures the average intensity transfer function of the fiber.

Chromatic delay in light emitting diodes.

When the current through the junction of a light emitting diode (LED) is modulated, there is a delay between the modulation and the response of the optical signal to this modulation. We have recently observed that this delay is not the same at different parts of the LED's optical spectrum. This effect, the relative delay between spectral components, we call chromatic delay. This paper reports the results of measurements of chromatic delay for several LED's of various kinds. This effect amounts to delays of the order of 200-300 psec between half power points of the LED spectrum. Thus it establishes a lower limit on the rise time achievable from these devices.

Transmission characteristics of three corning multimode optical fibers.

The loss spectra, refractive-index profiles, numerical apertures, and pulse dispersion characteristics of three multimode optical fibers made by Corning Glass Works have been measured at Bell Laboratories. The lowest transmission loss, 4.3-6.8 dB/km, was observed at 1.06-microm wavelength; in the 0.8-0.9-microm spectral region the losses ranged from 6.6 dB/km to 11.6 dB/km. The numerical apertures of the fibers, designated as Nos. 1, 2, and 3, were calculated from the measured refractive-index differences to be 0.133, 0.157, and 0.121, respectively. Pulse dispersion due to multimode effects in fiber No. 1 (1 km long) was 8.4 nsec at 0.9-microm wavelength; the values were 6.0 nsec for fiber No. 2 (0.363 km long) and 2.6 nsec for fiber No. 3 (0.290Km).