A 24-hour periodicity in the activity of a nickel-coated glass slide used for carrying out immunologic reactions at a liquid-solid interface.

Active nickel-plated slides are prepared by evaporating the metal in the presence of a magnetic field oriented perpendicularly to the slide, the surface being metallized facing the south pole of the field. Active slides coated with an antigen layer (bovine albumin or ovalbumin) can specifically adsorb a layer of antibodies nearly twice as thick (70 to 80 A) as that adsorbed on inactive slides (40 A). The activity of a slide varies within a 24-hour period. Fully active at night, a slide gradually loses its activity from sunrise on but regains it at sunset. The experimental evidence favors the view that inactivation is brought about by soft cosmic rays emanating from the sun. The inactivation can be prevented by keeping the slide under 3.5 cm of lead.