Abstract
By means of the apparatus described by Hinrichs, ultraviolet point radiation was used to locally modify the development of chick embryos. 1 At various intervals during incubation, eggs were opened, 2 and the desired region exposed for a given period of time, after which the shell was again sealed shut, and the incubation continued.
Most of the present experiments were made on the developing eye, and results were obtained as follows: (a) inhibition of the rate of development as compared with the unradiated eye, (b) killing of lens tissue, (c) stimulation of rate of pigment formation in the optic cup. The type of effect obtained depended on the dosage and the age of the embryo.
Exposures of the developing brain resulted as follows: short exposure of the forebrain of a 2-day embryo produced a lateral overgrowth on the exposed side. No such effect was obtained in the hindbrain. Longer exposures produced a coagulation of brain tissue. Exposure of the median posterior region of a 2-day embryo caused degeneration of that region.
Even moderate exposures of the heart (40 sec.) produced a slowing of the rate of beat in a 2-day chick, and on subsequent incubation, a loss of contractility of the exposed region.
An interesting condition was brought about following a 45-second exposure of the base of the aortic arches. On the exposed side, the arches atrophied as did also the tissues and organs supplied by them, while on the unradiated side, the arches and vessels were distended, appeared larger than normal, and the organs on that side of the body were completely normal in their development.
It was found that the developing tail and limb buds were relatively non-susceptible to moderate doses (45-60 sec.), while a 90-second exposure produced a coagulation of tissue in the hind limb of a 2-day chick.
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