1. The general aim of the investigations here reported has been to obtain evidence for or against "indirect" radiation effects.
2. To this end, twenty-six successful cross circulation experiments (carotid to carotid anastomoses) have been performed between normal cats and radiated cats.
3. Cross circulation was established in most instances at some specified time interval after the radiation of one partner. All intervals up to eighty-two hours after radiation of one partner were covered.
4. In seven experiments cross circulation was established and then one animal radiated while the other was shielded. These were considered the most critical experiments of the group.
5. Detailed data on leukocyte and lymphocyte counts in the normal animals obtained during an approximately twenty-eight day period of follow-up are presented.
6. These data are not considered to support the thesis of indirect effects peculiar to radiation. A trend toward slightly lowered absolute lymphocyte counts in normal animals after cross circulation was not considered significant, and in no instance did leukopenia develop in the normal animal.
7. The literature is reviewed and discussed.
ACKNOWLEDGEMENTS The authors gratefully acknowledge the assistance of Mr. Morey J. Wantman and the Division of Statistics for the statistical analyses and the valuable assistance of Miss Wilma Kujowski in translating the foreign literature.