Abstract
AS a consequence of the original work of Castaing1 on the electron beam micro-analyser, widespread application has been made in the field of physical metallurgy2. It is the purpose of the present communication to record the applicability of this technique to biological problems. In the Castaing instrument a beam of electrons, focused to a spot 1µ in diameter, excites fluorescent or secondary X-rays in the specimen, which are analysed in a crystal spectrometer with Geiger counter detection. An optical microscope with a reflecting objective permits simultaneous viewing and analysis of the irradiated spot. Mechanical stage motion allows the selection for analysis of any desired spot in the specimen. The range of elements at present detectable coincides with that of modern X-ray spectrographs, that is, elements lying above sodium in the Periodic Table. Two characteristics of these instruments of paramount importance to biological research are: (1) a detectable limit as low as 10−14 gm.; (2) spatial resolution of approximately 1µ. Birks has recently discussed the electron probe instrument in its numerous modifications3.
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