The appearance of labeled cells in the thoracic duct lymph of the guinea pig after the administration of tritiated thymidine.

By N. B. EVERErF, W. 0. REINHARDT AND J. M. YOFFEY#{176} V ARIOUS LABELING methods have been used in an effort to elucidate the life history of the different groups of leukocytes. Detailed references to the literature will he fotinti elsewhere ( AntIreasen anti Ottesen2a; Boyd, Casarett, Altman, Noonan anti SalomanT; Farr’ 4; Weisberger, Guyton, Heinle anti Storaasli42; Osgood, Tivey, Davison, Seaman and Li25; Kline and Cliffton24; Fichtelius’5; Ottesen2’; Leahy, McNickle and Smith27; Yoffey and Courtice4 ; Hamilton21; Craddock’#{176}; Ellis, Lajtha and Oliver’3; Yoffey, Hanks and Kelly45; Hansen22 ) . The experiments fall into two main groups. In the first group, cells are obtained from one animal and injected into another. Labeling of the cells may be affecteti in vivo, while they are still in the dcnor animal, or in vitro, after they’ have been removed from the donor. In either case it is difficult to know w’hether or not, as a result of the manipulations, the cells finally transfused may not have suffered some degree of damage. Even when there is no obvious sign of damage, there may still have been some interference with the normal developmental cycle, or the cells may have been obtained at the wrong stage of development. In the second group of experiments the cells are labeled in vivo, in the animal in which they are being studied. This type of labeling would seem to be more physiologic, and to give rise to the minimum of interference with the normal life cycle of the cell. Labeling is most frequently effected by means of a radioactive substance which has a special affinity for some cell constituent, and which can subsequently be identified either after chemical extraction or in autographs. In the case of the lymphocyte, the isotopes used are such as are believed to be incorporated into the DNA. Most workers have used 32 ( e.g., Andreasen and Ottesen,2’3 Weisberger et al.,12 Osgood et al.,28 Kline and Clifton,24 Fichtelius,’5 Ottesen,2#{176} Craddock,1#{176} Yoffey et al.,45 Perry et al.,32’33). Boyd et al.7 used C14, as also did Hamilton,21 who administered C’4-orotic acid; Ellis, Lajtha and Oliver13 employed S3 .