The Relations of the Interstitial Cells of Leydig to the Production of an Internal Secretion by the Mammalian Testis

The questions considered in this paper are, " Does the mammalian ~esticle, in addition to the formation of sperm, furnish an internal secretion essential to the normal development of the organism?" and, " I f so, which cells of the testicle have this function ?" The testicle is well suited for such a study, both from its anatomic relations and from its histologic structure. It is easily accessible to experimental manipulations, and natural abnormal placements of the organ are not uncommon, entailing characteristic changes of structure which greatly aid in analyzing the possible functions of its several component elements. Historical.--Despite the statements to the contrary by several writers (yon Lenhoss6k, 1897, Plato, 1896, Bouin et Ancel, I9O3), Leydig ( i85o) , and not K611iker ( I854) , first described the presence of characteristic cells lying within the interstices of the seminiferous tubules. KSlliker's careful histological study of the interstitial cells appeared four years later. He characterized these structures as clear round cells, analogous to embryonic connective tisst~e, vacuolated, and containing fat and pigment granules. An important fact pointed out by K611iker, and one too little considered in certain theories which have been advanced to explain the functions of the interstitial cells, is the constant presence of these cells not only in the interstices of the seminKerous tubules, but in the