Historadiography

IN RADIOLOGIC routine, natural or artificial differences of density must exist in order to obtain shadows which can be interpreted. In operating in the usual way, under 50 kv. potential, rarely is one able to differentiate tissues which are of nearly the same density. Also, the grain of extremely rapid x-ray films is always very large and can hardly support enlargement. The thickness of the tissues examined is such that diffused rays play an important rôle. When the object to be examined is thin and non-dense, it is necessary to lower the voltage, i.e., to lessen the mean wave length of the x-ray beam; which at once gives rise to difficulties. Goby (1913–1925) presented, before L' Académie des Sciences, radiographs of small objects and insects taken with soft rays. His work, although of interest, did not bring about any change in the usual technic of x-rays. Under atmospheric pressure, absorption phenomena prevented Goby from making use of the advantages which many soft rays afford in differentiating bodies of neighboring densities. The diffusion of the air played an important rôle and, on the other hand, enlargements could scarcely exceed one-tenth of some diameters. It was of interest to try to take radiographs of more delicate structures than those studied by Goby. In 1930, Dauvilliers presented a note on radiomicrophotography. He was the first to utilize grainless photographic plates; the negative thus obtained could be greatly enlarged. Using very soft rays he obtained interesting contrasts at a potential of from 7 to 9 kv. To avoid air absorption, the plate and preparation were placed in a special camera through which a current of hydrogen was passed. It seems interesting to us to recall briefly Dauvilliers' technic, which we have modified slightly. He used a tube which he had made for crystal analysis. It consisted ofa metallic bodyfortheanodewithan interchangeable target bearing four diaphragms of variable diameters, shut off by aluminium windows which could be attached to hermetically sealed cameras bearing the photographic plates. These cameras were emptied or filled with hydrogen. A pin hole central focus was obtained by means of a Coolidge cathode. The vacuum in the tube was maintained during the manipulations by an oil diffusion vapor pump. The potential applied varied between 7 and 8 kv., with a tungsten target and a current of 0.1 ampere; the time of exposure did not exceed two hours. The plates were reinforced with silver in order to obtain photographic densities which would support greater enlargements. The preparation is applied directly to the emulsion with a drop of alcohol. After exposure the preparation is removed and the plate is developed and examined under a microscope. By this method Dauvilliers obtained a fine radiomicrograph of the pith of elder, in which intercellular separations belonging to the microscopic skeleton are perfectly discernible. Personal Technic.