vi PREGNANCY PARTURITION PUERPERIUM 249 



connection with the uterine walls, becomes an extraneous body, 

 and every contraction of the uterus helps to expel it." 



Spiegelberg, in order to explain why the various conditions 

 we have enumerated bring about parturition exactly at the end 

 of the fortieth week of gestation, advanced the hypothesis that 

 the real cause of parturition must be the maturity of the foetus, 

 which, during its development, utilises certain special chemical 

 substances of an unknown nature, and ceases to utilise them 

 as soon as it has reached maturity ; these substances are then 

 reabsorbed by the maternal blood, in which they act as hormones, 

 capable of exciting all the nervous and muscular mechanisms 

 which effect the expulsion of the foetus. We have mentioned 

 that with the involuntary uterine contractions there are associated 



5 Minuter 



FIG. 107. Curve of pressure and of contraction of uterus during the period of expulsion. 

 (Schatz, Arch. f. Gyn. iii.) Synergic action of pressure and contraction. The apices of the 

 curve coincide with the abdominal pressure. 



in the last stage' of parturition voluntary contractions of the 

 abdominal muscles, which, by increasing the intra-abdominal 

 pressure, support the uterine contractions and force the contents 

 of the uterus towards the canal, which offers the least resistance 

 to the total intra-uterine pressure. 



Schatz has succeeded by his manometric method in recording 

 the curves of the abdominal pressure associated with the uterine 

 contractions during the period of expulsion (Fig. 107). We refer 

 the reader to treatises on obstetrics for details concerning the 

 passive dilatation which takes place in the cervix of the uterus, the 

 vagina, vulva and perineum during the final act of parturition, 

 the way in which natural parturition takes place according to the 

 different presentations of the foetal head, and the artificial aids 

 which are necessary for delivery in cases of difficult labour (distocia), 

 which are usually caused by abnormal presentations of the head 

 of the foetus. 



