204 INTERNAL SECRETIONS OF THE OVARY 



theories may be evolved: (a) that the ovary in its immediate 

 pre-partum state exerts a stimulating action on the posterior 

 pituitary which then secretes more oxytocin, or (b) that the 

 immediate pre-partum ovary increases the sensitivity of the 

 uterus to the posterior pituitary. 



Influence of the ovary on the posterior pituitary body. With 

 the former of these ideas in view Dixon and Marshall (i6i) in- 

 vestigated the effects on the posterior pituitary body secretion of 

 extracts of ovaries at various stages of the cycle. These experi- 

 ments were performed upon the dog, and consisted in the 

 collection of the cerebro-spinal fluid before and after the 

 injection of ovarian extracts, and in the assay of the cerebro- 

 spinal fluid samples for their oxy toxic action. As a result of 

 these experiments, Dixon and Marshall concluded that the ovary 

 at a certain stage of its cycle, when the corpora lutea were in 

 regression, elaborated some secretion which stimulated the 

 posterior pituitary body. They considered a similar action at 

 the end of pregnancy to be a vital factor in the mechanism 

 of parturition. Many criticisms have, however, been levelled 

 against these experiments, for instance by Swale Vincent 

 (623). In the first place, doubt exists as to whether the 

 posterior pituitary body actually secretes into the cerebro-spinal 

 fluid, and in any case Dyke and Kraft (174) found no changes in 

 the oxytoxic properties of the cerebro-spinal fluid during labour. 

 Secondly, various tissue extracts may affect the secretion of the 

 posterior pituitary, and thirdly, Blau and Hancher (69) 

 entirely failed to confirm Dixon and Marshall's results. Addis 

 (i), however, appears to have obtained some clinical results 

 in keeping with the hypothesis. 



Effect of the corpus luteuni on sensitivity of the uterus to oxytocin. 

 The evidence that the pre-partum ovary stimulates the secretion 

 of the posterior pituitary is not, therefore, conclusive. On the 

 other hand, the evidence that the uterus has a cyclic suscepti- 

 bility to oxytocin does seem to be conclusive. Knaus (326) 

 found that abortion can only be produced in the rabbit by the 

 injection of posterior pituitary substance during the last few 

 days of pregnancy; earlier than this no result follows the 

 administration of even large amounts. In confirmation of this 

 result, Knaus (328), as an extension of the work referred to 



