The absorption of antibodies from immune sera by the gut of the young rat

Antibodies from immune rat serum administered by mouth to young rats up to 18 days of age pass readily into the circulation. Thereafter the capacity to absorb antibodies from the gut declines rapidly and could not be detected beyond 21 days of age. Antibody could be detected in the circulation of the young rat within $\frac{1}{2}\text{h}$ of administration and had reached a maximum concentration in 3 h. Immune sera prepared in mice, rabbits, cows and fowl were administered also and the results were compared with those obtained with immune sera prepared in rats. Agglutinins prepared in mice entered nearly as freely as those prepared in rats; those prepared in rabbits significantly more slowly than either. Agglutinins prepared in cows or in fowl did not appear to enter at all within the limits of the sensitivity of the technique. Incomplete agglutinins to sheep red cells prepared in rats entered as readily as complete agglutinins to Salmonella pullorum prepared also in rats.