Groups of young adult rats were inoculated with bovine serum albumin in complete Freund's adjuvant into one foot-pad, a cervical lymph node, the spleen, a forelimb muscle, the cavity of the mediastinum or directly into the thymus. Arthus responses and circulating antibodies occurred in decreasing intensity in the order listed, but marked delayed sensitization resulted in the foot-pad and lymph node groups only.
Groups of guinea-pigs were inoculated with egg albumin in complete Freund's adjuvant into a foot-pad, on the surface of the thymus or into the thymus. Delayed sensitization did not develop until the 17th day in the intrathymic group, and Arthus reactions and circulating antibodies were poor when compared with the other animals.
Allergic encephalomyelitis was found in all seven rats injected with spinal cord and adjuvant in one foot-pad and in five of seven animals injected into a cervical node, while a single minimal lesion was present in one of twelve animals inoculated into the thymus directly.
Plasma cells were seen in the thymus after injection of protein and adjuvant near the connective tissue of the capsule, the interlobular septa and blood vessels, whereas nervous tissue and adjuvant produced virtually no plasma-cell response.