INTERNAL SECRETIONS 109 



In each of these species there is present at the end of {)seuclo- 

 pregnancy a persistent corpus hit eum in a condition of involution 

 not dissimilar to that of the corpus luteum veruni at the end 

 of true pregnancy. Further, pseudo-pregnancy can only occur 

 when a corpus luteum is present. Moreover, all these animals 

 display habits and instincts at the end of pseudo-pregnancy 

 which are identical with or similar to those associated with 

 imrturition. Thus the bitch may prepare a bed as if for a litter 

 of pups, the doe rabbit plucks her breast of fur and uses it to line 

 a nest (Hammond), and the female marsupial cat cleans out her 

 pouch as though for the reception of young (Hill and O'Donoghue). 

 It has been shown that the occurrence and duration of pseudo- 

 pregnancy are dependent on the corpus luteum, and consequently 

 it is exceedingly })robable that the processes associated with 

 parturition are similarly correlated witli changes in the amount or 

 character of the ovarian secretions. 



The manner in which the ovary influences the uterine con- 

 tractions has recently formed the subject of experimental in- 

 vestigation (Dixon and Marshall), and evidence has been adduced 

 to show that it may act through the intermediation of the posterior 

 lobe of the pituitary gland (a small organ lying underneath the 

 third ventricle of the brain). It is well known that extract of 

 this organ promotes uterine contraction, and that it is used 

 practically by obstetricians to expedite labour, especially in cases 

 of difficulty. Owing to its exceptionally powerful effect, pituitary 

 extract must be used with great caution, as it may produce " con- 

 traction rings " on the foetus, which is consequently born dead. 

 It has now been shown that ovarian extract may promote pituitary 

 secretion, as manifested by the effect of the substance obtained 

 by drawing off samples of cerebro-spinal fluid after injecting 

 ovarian extract into the circulation. It had already been shown 

 that the pituitary gland secretes, its active principle into the 

 cerebro-spinal canal, whence it passes into the vascular system and 

 is distributed throughout the body. In the experiments referred 

 to, extracts of rabbits' and sows' ovaries were obtained at different 

 periods of pregnancy and of the oestrous cycle, and injected into 

 a dog ; samples of the cerebro-spinal fluid were then drawn off 

 from the dog and tested upon guinea-pigs' uteri suspended in 

 Ringer's solution (a saline fluid resembling blood serum), and 

 the degree (if any) of the contraction of the uterus duly observed 



