and may have been at his insistence. These serial numbers were on the top of the guard, or sometimes the inner barrel. There were no razor serial numbers from 1931 until 1951.

Razor Date Codes began in 1951 and used the same system blades had used since 1931, a code that identified the year and calendar quarter of manufacture. These codes are found on the underside of the guard mechanism, or in cartridge razors, near the attachment mechanism for the blade.

Gillette Blade Date Codes (and earlier lot systems) were imprinted on one side of the blade as a series of letters and/ or numbers, or on the cartridge. The blade system adopted in 1931 is still in use today, and was used on razors as well after 1950. Allolfactory nerve stimulation exhibited a simple monophasic waveform that lasted for a few seconds. At embryonic 9-day stage, the optical signal became multi-phasic, and the oscillatory event was detected in some preparations. The oscillation was restricted to the distal half of the olfactory bulb. As development proceeded, the incidence and duration of the oscillation gradually increased, and the waveform became complicated. In some cases at embryonic 12-day stage, the oscillation lasted for nearly a minute. The frequency of the oscillation increased slightly with development, but it remained in the range of theta oscillation during the 9- to 12-day stages. We discuss the ontogenetic dynamics of the oscillation and the significance of this activity in the developing olfactory bulb.