. Radium, X rays and the living cell. llother forms of lymphoid tissue themeshwork supporting thelymphatic cellular elements is composed of connecti\-e {) tissue cells and fibres ; in the thymus this is not thecase ; the reticulum of the lobules consists of cells more or lessstellate in form, whose branches anastomose freely to form thesupporting meshwork, and which are derived from the epitheliumhning the third embryonic branchial cleft ; thus accoimting for THYMUS AND THYROID 205 the observation of Regaud and Cremieu that under certain con-ditions of irradiation these reticula
. Radium, X rays and the living cell. llother forms of lymphoid tissue themeshwork supporting thelymphatic cellular elements is composed of connecti\-e {) tissue cells and fibres ; in the thymus this is not thecase ; the reticulum of the lobules consists of cells more or lessstellate in form, whose branches anastomose freely to form thesupporting meshwork, and which are derived from the epitheliumhning the third embryonic branchial cleft ; thus accoimting for THYMUS AND THYROID 205 the observation of Regaud and Cremieu that under certain con-ditions of irradiation these reticular cells revert to an epithelioidtype. One other element of the thymus must be noticed, theHassalls corpuscles. These are rounded structures of con-centrically arranged cells, and situated at the centre of thelobules. By most authorities they are regarded as being special-ised forms of the reticular cells ; though Pigache and Beclereregard them as of lymphocytic origin. In the present account of the effect of the X rays upon the KFr RK Fig. 34.—Rabbit, portioa of surface of thymus, irradiated 5 hours. Killed half an hourafter exposure was finished. Section shows the different stages of lymphocyte destruction. L, unaffected L, lymphocytes with pycnotic nuclei. KL, lymphocytes containing dark masses ofchromatin. K/r, fragments of nuclei. i?iC, reticulum nuclei. M, empty reticulum (masche). Archiv fiir Anatomic. 1907. thymus, the work of different observers must be consideredseparately ; not only because different kinds of animal wereused, but on account of variations in the technique of regards the broad outlines of the retrogressive changes whichthe organ undergoes as a result of exposure, there is very fairagreement ; but the final results differ according to the durationand method of irradiation. The first extensive and systematic series of observations uponthe effect of X rays on the thymus are those of Rudberg (1907). 2o6 THYMUS AND THY
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