RADIATION IN PRENATAL DEVELOPMENT 889 



indicate differential sensitivity throughout the body. The mother's 

 uterus was exposed by laparotomy and a localized beam (0.5-3 mm diam- 

 eter — see 1943a for technique) directed from below at the head region of 

 the embryos, particularly at the base of the diencephalon. The trav- 

 ersed region also included the central shaft of the cranium, the buccal 

 cavity, and the primordium of the tongue. The dose range was 5000- 

 200,000 r. The investigators confined exposures to mouse embryos of a 

 certain age, namely, 12 days 6 hours, adding occasionally a second 

 irradiation 24 hours later. All observations were made just before term. 

 In three publications (1943b, 1947a, c), the authors report on effects in 

 structures directly traversed by the pencil of X rays; in another three 

 (1947b, 1949a, b), they describe observations on the reproductive system 

 which was not irradiated but could conceivably have been secondarily 

 affected as a result of pituitary damage. 



As expected for the high doses used, there was considerable damage in 

 the radiation path. Externally, the animals treated with 5000 40,000 r 

 were microcephalic, often had open eyelids, and occasionally lacked ears, 

 tongue, salivary glands, or upper or lower jaws. After irradiation with 

 190,000 r, the head at term was only a small atrophic mass. Condensa- 

 tion of mesenchyme to precartilage was suspended and membranous 

 ossification suppressed even with 5000-40,000 r. The same dose range 

 produced extensive cerebral lesions, and complete destruction of the optic 

 nerve and of both layers of the retina. Following treatment with 

 60,000 r, the brain at term showed the vesicle configuration characteristic 

 of the stage of irradiation; while 190,000 r left only a necrotic mass with 

 the vesicles no longer recognizable. Complete destruction of the anterior 

 lobe of the pituitary could be achieved only with 200,000 r divided evenly 

 between 12 days 6 hours and 13 days 6 hours. It should be noted that, in 

 spite of the massive damage due to the high doses used, it is possible to 

 find in the data evidence of differential susceptibility of different struc- 

 tures. Thus, only a quarter (or less ?) of the dose required to inactivate 

 the anterior lobe will completely eliminate the pars nervosa; the choroid 

 plexus resists 60,000 r, a dose which causes almost complete destruction of 

 the rest of the brain; the lens of the eye resists doses which completely 

 destroy retina and optic nerve. 



Several indirect changes were noted in regions presumably not trav- 

 ersed by radiation. Effects on body size have already been discussed 

 (see p. 877). In addition, there was marked atrophy of the adrenal 

 cortex and a reduction in liver glycogen. In spite of pituitary destruc- 

 tion, the histogenesis of the genital tract, including accessory structures, 

 and the cytological differentiation of the germ cells proceeded normally, 

 which led the authors to suggest that either the hypophysis exerts no 

 gonadotropic influence in development or that its function can be taken 

 over by maternal or placental hormones. There was, however, up to 



