Certain tentative conclusions may be drawn regarding the relationship between the involution of the thymus gland and the gonads in the fowl.
(1) At maturity the male possesses thymus substance considerably greater in amount than that characteristic of the female.
(2) Successful ovarian grafting in complete males induces a female grade involution of the thymus.
Intermediate grades between male and female thymus follow the implantation of ovary to males in certain cases, although in these no grafts were recovered at the post-mortem examination.
Since only small ovarian grafts have been recovered from males with a female type of thymus, it is evident that the reaction is a delicately balanced one requiring only a relatively small amount of ovarian tissue to determine the degree of involution.
(3) Partial ovariotomy, when performed before sexual maturity, produces no deviation from the female type of thymus.
(4) Castration and ovariotomy cause a delay in the involution of the thymus.
(5) Successful implantation of testes to complete males has no effect on the size of the thymus.
(6) No inference may be drawn from the results of partial castration and the degree of thymus involution.
(7) A definite relationship exists between gonad and thymus involution in the fowl.