[Mastocytes in the rat thymus].

The distribution and the histochemical characteristics of the thymus mastocytes of postpuberal rats have been studied, in different experimental conditions (control, castrated, castrated and treated with testosterone, and fatigued rats). The results may be summarized as follows: 1) Mastocytes have been found only in the thymic capsule and connective tissue septa : they have never been observed among the parenchymal cells. 2) In the thymus of castrated rats the total number of mastocytes is significantly reduced. 3) In the thymus of the rats castrated and treated with testosterone, the total number of mastocytes, in comparison to the castrated rats, increases in a statistically significant way. A slight increase was observed also in comparison to the controls. 4) In the thymus of the fatigued rats a statistically significant increase of the number of mastocytes has been observed. 5) In the sinuses of the parathymic lymphnodes, numerous mastocytes and some cells that for their histochemical characteristics can be regarded as immature mastocytes, have been found.