Abstract
The extraordinary separation of the pubic bones of the guinea pig in late pregnancy has been recorded by several investigators. Todd 1 has made the most recent contribution to this subject and has thoroughly discussed previous research as well as described the gradual changes that take place at the symphysis during normal pregnancy and the subsequent return to the post-parturient condition typical of multiparous females. The writer has been interested in this phenomena for the last four years, chiefly from the standpoint of its physiological explanation and possible correlation with a similar condition which has been studied in the pocket gopher. 2 In the pocket gopher the pubic bones are resorbed at the symphysis before pregnancy occurs, and the reaction is governed by the ovary, while in the guinea pig relaxation of the pubis occurs during pregnancy and little or no bone is resorbed, but the connective tissue at the symphysis is greatly increased, allowing a marked separation of the bones.
It has been possible to produce changes in the pubic ligament of virgin guinea pigs by experimental procedure and these are apparently identical with those occurring normally during pregnancy. If 2 cc. of blood serum of pregnant rabbits or guinea pigs are injected subcutaneously into virgin guinea pigs during early post oestrum a noticeable relaxation of the pubic ligament can be discerned within six to eight hours by movements at the pubis. These movements gradually become more pronounced during the next eighteen hours and the ligament may not return to its normal condition for two or three days. The blood of males and nonpregnant females does not bring about this reaction, and the blood of parturient females loses its effectiveness very noticeably within the first eight hours, negative results being usually obtained from blood drawn 24 hours after the young are born.
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