182 SECTIONAL ADDRESSES. 



uterus supersensitive and highly responsive to other forms of stimu- 

 lation. 



The pituitary secretion passes either entirely or mainly into the cerebro- 

 spinal fluid. Histological examination has shown that the gland is 

 suspended in a bath of cerebro-spinal fluid and has an opening, at least in 

 some animals, directly communicating with this fluid. Since the experi- 

 ments of Marshall and myself this secretion of pituitary into the cerebro- 

 spinal fluid has been confirmed many times, more particularly by 

 Trendelenburg, Janassy and Horvath, Miura and Siegert. The reason 

 some investigators have failed to find pituitrin in the cerebro-spinal 

 fluid is because they have tapped the theca too low in the spinal axis. 

 Pituitrin after excretion is rapidly absorbed and never reaches beyond 

 the cervical cord. It has been suggested that the secretion of oxytoxic 

 substance is not really pituitrin, but some other substance, and to this 

 it can only be replied that it exerts every known chemical and physio- 

 logical action of posterior lobe extracts. In my Dohme Lectures I gave 

 the last piece of evidence in this respect by showing that it also exerts 

 the melanophore dilator action on the frog, an effect which, so far as 

 I know, is quite specific. Trendelenburg has also described this action. 



The pituitary gland is intimately connected with the phenomenon of 

 pregnancy ; statistics show that the size and weight of the gland in men 

 and nulliparae are about the same ; in primiparae the weight has increased 

 by about 50 per cent, and in multiparse by about 90 per cent., though 

 most of the increased weight is due to the anterior lobe. 



The posterior pituitary substance has at least three actions of import- 

 ance in medicine : it inhibits the secretion of urine, it has an antagonistic 

 action to the insulin effect, and it sensitises and, in larger doses, contracts 

 the plain muscle of the uterus. The last action is so profound that it 

 overshadows all the other muscular effects, and pituitrin may be said 

 to have a true specific action on uterine muscle in rendering it super- 

 sensitive to every form of extraneous stimulus. 



Our experiments showed that at one stage only of the ovarian cycle 

 was this hormone elaborated, namely, at the stage when the corpora 

 lutea are degenerating. So long as the corpora are functioning they 

 control the metabolism of the ovary, but when they degenerate control 

 is lost and the ovary liberates the specific substance which excites the 

 pituitary gland to secrete. This means that extracts of the ovary made 

 between the heat periods or during pregnancy are without effect on the 

 pituitary gland, but extracts made just before the heat period or just 

 before parturition induce secretion of the gland. As the significant action 

 of pituitary extract is to sensitise the uterus it is difficult, if not impossible, 

 to avoid the conclusion that these two phenomena are closely associated. 



It is well known that substances introduced into the cerebro-spinal 

 fluid find their way almost immediately into the blood, and hence it might 

 be expected that extracts made from the blood of pregnant rabbits 

 obtained at the time of delivery would have a contractile influence on 

 the uterus ; this has been found to occur. Similarly blood obtained 

 from pregnant women at the time of delivery contracts the guinea-pig's 

 uterus to a considerably greater degree than normal blood. Mayer 

 collected the cerebro-spinal fluid from women during Csesarean section. 



