Abstract
In a series of papers, the first of which appeared in 1912, Tschachotin 1 described a method of focussing ultraviolet radiation into a cell by means of a system of quartz oculars and objectives in a microscope. The following experiments make use of a principle well-known to physicists, and recently demonstrated by Wolf 2 to be of value in biological experiment, namely that ultraviolet radiation will follow a quartz rod, be it straight or bent, because of internal reflection. If the rod is drawn out to a fine point, radiation effects may be limited to a small area.
As will be seen from the accompanying sketch, a quartz rod was placed at right angles and close to the burner of a mercury-vapor lamp. A shutter control was interposed between the rod and the burner. The length of the rod was 29 cm. with a 45° bend at 1.0 cm. from the tip. (In order to minimize “leakage”, the area just above the tip was painted with opaque paint, or in some cases covered with a glass cap.) The rod was held in place by a universal joint, as indicated, and was freely movable in all directions. A very small change of position at the fixed end afforded considerable range of movement at the free end. A movable stage, not indicated in the diagram, aided in focussing the radiation on the desired spot on the heart.
The experimental material was young Fundulus heteroclitus, a small salt-water minnow. Shortly after hatching, the body wall is still transparent so that heart movements can be studied through it. The animals were quieted with a sea-water solution of chloretone, and turned ventral side up.
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