Abstract
The amount of radiation from a mercury quartz arc required to produce an erythema of a certain skin area of a certain individual is, as a rule, greater the more this area has been exposed to ultraviolet light of wavelength 240 to 310 mμ (the region responsible for the reaction) during the previous 2 months. Evidently some change has been produced in the skin by the first irradiation which makes it less sensitive to the following exposure. What change is responsible for this protection is not definitely known, but it has been shown that it is a local change extending over the exposed area and slightly beyond the margin. It has also been proven that it does not run parallel to the tanning which is another effect produced by certain ultraviolet light bands between 240 and 370 mμ. 1
For treatments with ultraviolet light it is important to know when and to what extent such protection is produced. Some experiments along this line have been carried out by other investigators and we have attempted to check their measurements and to contribute some further details. 2
The development and the consequent progress of the protection varies in different individuals, but the general characteristics of the course seem to be the same for most persons. Some exceptions have been noticed and this fact must be kept in mind as such exceptions are apt to be more common among patients than among healthy individuals.
We have experimented with 3 healthy individuals and the main procedure has been to irradiate one fair-sized area and then to repeat the irradiation at different times to different parts of this region. A new Victor mercury arc lamp was used without any filter. The current was 4.5 amperes at 65 volts and the distance from burner to skin 30 inches.
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