| Abstract: | By fractionation of calf thymus extract No. 1A, prepared by the method of Goldstein et al., on a column with Sephadex G-25 a fraction stimulating antibody formation in newborn animals was obtained. Tests of the activity of analogous fractions of extracts of calf tonsils, spleen, lymph glands, and liver suggested that the thymus is the sole source of a specific humoral factor stimulating antibody formation which may accumulate in peripheral lymphoid structures. The low activity of tonsillar extracts does not confirm the hypothetical role of the tonsil as the central organ of immunity, corresponding to the bursa of Fabricius. |
