The effect of local beta irradiation from an external source upon the growth of the bones and some other tissues of rats.

One-day-old rats were subjected to one-half (anterior or posterior) body irradiation by the beta rays of P. The skin exposure on the body was about 1,700 to 2,000 rep. The skin exposure on the tail, hands, feet, forearm, and leg was somewhat less than twice this. The animals were sacrificed at 200 days of age. No cutaneous tumors occurred. The irradiated animals weighed 5 to 10 per cent less than the controls. Males and females reacted alike. Changes were observed only in the part directly irradiated. The "anterior" animals had significantly smaller ears, skulls, and forelimbs; the "posterior" animals, tails, hindlimbs, and testes. Skeletal measurements are given. No effect was observed on the stomach, kidneys, liver, or heart. > ; i ;■■■• ; ' ■'/,.. -■''"■ ( ) The technics of external irradiation with beta rays have been presented by Raper, Zirkle, and Barnes, and the gross effects following total-body irradiation were reviewed by Raper. In the case of the 1.7 Mev beta rays from P, 95 per cent absorption occurs in 2.9 mm of soft tissue, and consequently their effects are limited to the skin in animals the size of rats, or larger. Such effects include epilation, ulceration, and tumor induction (Henshaw, Snider, and Riley). In the case of the mouse, however, penetration beyond the skin is appreciable, and Snider found damage, upon histological examination, to one side of the spleen, one side of the testis, and in the marrow of the bones of the feet. It was obvious that baby rats would also show damage to the deep tissues. Stapleton (unpublished experiments) compared the acute lethal effects of total and partial body exposure to P beta rays in the one-day old rat. For partial body exposure, the anterior or posterior half of the animal was employed. We have raised the survivors from some of these experiments, and have examined the relative growth of a number of organs, especially the bones. As might be anticipated, the parts irradiated show definite inhibitions of growth. The degree of inhibition exhibited by an organ correlated fairly well with its depth below the surface at the time of irradiation. The effects were local; inhibition of growth of the posterior half of the animal was without gross effect upon the anterior.