no INTRODUCTION TO SEXUAL PHYSIOLOGY 



and recorded. It was found that of the various substances 

 employed (testis, epididymis, pancreas, corpus luteum, etc.), 

 extract of ovary alone had a positive effect, but only if the ovaries 

 employed did not contain fully formed and presumably active 

 corpora lutea. Ovaries throughout pregnancy gave a uniformly 

 negative result until near the end of the period, when the uterus 

 (acted on through the intermediation of the pituitary) became 

 increasingly excited as the end of the gestation period was 

 approached. The most extensive uterine contractions occurred as 

 a result of employing ovarian extract obtained just about the date 

 when parturition was due. It is suggested, therefore, that the 

 excitatory mechanism of the ovary is inhibited during pregnancy 

 when the corpus luteum dominates the ovarian metabolism, 

 but that as this structure regresses the normal secretion is once 

 more formed in sufficient quantity to produce a stinmlus which 

 reaches and passes the threshold, and so, working through the 

 pituitary, brings about those uterine contractions which are the 

 immediate cause of birth. It was found also that extract made 

 from ovaries at the heat periods (when corpora lutea are absent), 

 and utiHsed in the same manner, likewise promoted uterine con- 

 traction, an observation which conforms with the experience that 

 pains resembling those of labour may occur in association with 

 menstruation. Extract of ovary containing developed luteal 

 tissue, whether or not the animal from which it was obtained 

 was pregnant, invariably led to a negative result. These results 

 are at any rate suggestive. 



The Gonads cmd the Other Organs of Internal Secretion. — It 

 is as yet impossible to formulate any general scheme to describe 

 the relation between the gonads and the other organs of internal 

 secretion, and such facts as are definitely known must, for the 

 present, remain isolated. It has just been shown that there is 

 probably some correlation between the ovarian cycle and the 

 activity of the posterior lobe of the })ituitary. It has long been 

 recognised that the thyroid gland is very liable to enlargement 

 at menstruation as well as during pregnancy, and that the swelling 

 at the time of puberty may sometimes lead to goitre. It is also 

 stated that the sexual act and marriage, in both sexes, may 

 increase the activity of this gland (M'Carrison). There is also 

 some evidence of a correlation between the suprarenals and the 

 gonads. Thus it is stated that in rabbits the suprarenal cortex 



