ee 1. Gastrointestinal Tract There have been few experiments where the gastrointestinal tract has been exposed in a manner similar to the one assumed here. In:one experiment currently underway at the Medical Center of the Oak Ridge Institute of Nuclear Studies, the dosimetry is being studied in dogs using Yittrium-90. The preliminary data are in reasonable agreement with the model proposed in reference one .° In another experiment,| rats were fed 1.0 to 6.0 millicuries of Yittrium-90 in a single feeding. Four of the 33 animals died of adeno- carcinoma of the colon and additional animale died with acute and chronic ulceration of the colon. A second group of rats was given 0.46, 0.20, or 0.06 me of Y7 per feeding over a period of three months with total accumulated amounts of 31.2, 15.6 and 4.68 mc respectively. Six of the eight animals at the two higher levels died with carcinoma of the colon and no malignancies were observed at the lowest level. The authars made no estimate of radiation doses. 3 In another experiment, DOE ARCHIVES rats were kept alive by the use of parabiosis or para-aminoproprio phenone either pre or post whole-body irradiation of 700-1000 roentgens. Four of the 21 rats developed tumors along the gastro- intestinal tract (one each jejunum, ileum, duodenum, and colon), with four additional animals showing tumors in other organs. However, in comparing gastrointestinal versus whole-body irradiation, the question has been raised as to a possible indirect carcinogenic action in the latter case 3 By using fast neutrons, lesser doses have been shown to produce an. appreciable percentage of intestinal carcinomas in mice, but this is not so relevant -9- Yd A