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Day-old chicks were bursectomized, growth rate, blood and spleen characteristics were examined and compared with those of sham-operated chicks of the same age at 3, 4, 5 and 6 weeks. Bursectomy was shown not to interfere with growth rate but to influence spleen weight at 5–6 weeks of age. No proliferation of pyroninophilic cells was noted but there was a decrease in germinal centers. At the age of 5–6 weeks lymphocyte numbers were reduced and heterophil numbers increased in the bursectomized birds.

IT HAS frequently been noted that the thymus of rapidly growing chickens is large, whereas that of slowly growing chickens is relatively very small. Ackert (1924) found that the thymus glands of chickens parasitized with Ascaridia perspicillum were smaller than those of non-parasitized chickens. However, Riddle and Krizenecky (1931) reported that the removal of both the thymus and the bursa Fabricius from 17 common pigeons did not affect development or function of the reproductive organs. They suggested that other organs, particularly lymph nodes, might have thymic functions. Plagge (1941) has concluded that the thymus glands of male and female albino rats are definitely sensitive to varying concentrations of sex hormones as indicated by gross changes in the thymus at puberty and by both gross and histological changes following castration or injections of sex hormones. Thymectomy does not affect the reproduction system of either sex. As the physiological relationship between the . . .

Glick (1955) observed that the weight of the bursa Fabricius at two weeks of age in White Leghorns (0.44 gm.) was larger (p In baby chicks of a randombred broiler-type strain, 72 to 92 percent of the variance in weight of the bursa of Fabricius at a constant body weight was attributable to genetic effects (Jaap, 1958). Since Chang, Rheins and Winter (1957) had demonstrated the importance of the bursa in antibody production, it appeared desirable to explore whether breed differences in bursa size existed at hatching. MATERIALS AND . . .