Enhancement of growth of chick host spleens following chorio-allantoic membrane grafts of homologous tissues.

T H E phenomenon of enlargement of the host chick embryo spleen, following grafts of homologous adult chicken tissues to the chorio-allantoic membrane (CAM), affords the investigator an excellent tool for the study of growth. Initial observations of this phenomenon were made by Danchakoff (1916) and Murphy (1916). Grafts of adult chicken spleen on the chorio-allantoic membrane of 9-day-old chick embryos brought about a striking enlargement of the host spleens after 8 additional days of incubation. The phenomenon was later studied by Ebert (1951), who showed that the effect was only partially organ-specific. Grafts of thymus and liver affected the weight of the host spleen, but in each case the effect was far smaller than that observed with splenic transplants. Andres (1955) found that injected kidney and liver debris, which elicited an increased mitotic index in the homologous host organ, was not inhibited in its action by killing the cells through freezing and subsequent thawing. Van Haeften (1958) recently reported hypertrophy of the embryonic host spleen following the administration of cell-free homogenates of spleen to the CAM. The above findings may be interpreted as being in accord with earlier template-antitemplate hypotheses (Weiss, 1947; Tyler, 1947): the introduced template, supplementing existing cellular templates, catalyse the formation of additional antitemplates leading to the enlargement of the homologous organ. Intact and proliferating cells as such, were sufficient but not necessary to produce the enlargement. Ebert (1954), using adult chicken spleen and kidney tissues labelled with S,