542 THE PHYSIOLOGY OF REPRODUCTION 



(7) Spiegelberg^ put forward the theory that parturition 

 was brought about through the action of substances secreted by 

 the foetus and passed into the maternal blood. These hypo- 

 thetical substances, which appear to have been comparable to 

 Starhng's hormones, were supposed to act on the uterine centre 

 in the spinal cord. Spiegelberg suggested, further, that the ex- 

 citing substances were elaborated as a result of an insuffi- 

 ciency of nutrition, and were an indication that the mature 

 foetus required other sustenance than that supphed to it 

 through the placenta. This theory appears to be devoid of all 

 experimental basis, but it is not opposed by any of the known 

 facts. 



(8) Tyler Smith,^ Minot,^ Beard * and others have held the 

 view that there is a connection between parturition and men- 

 struation, the two processes being physiologically homologous. 

 According to this theory, there is an increased tendency towards 

 uterine contractions at the periods at which menstruation would 

 occur if the condition were not one of pregnancy. Thus Tyler 

 Smith says that there is in aU women a greater tendency to 

 abort at the times represented by the catamenial periods. 

 According to Minot, the menstrual and gravitidal changes follow 

 the same cycle of events, the pregnant uterus passing through 

 a prolonged and intensified " menstrual cycle." Consequently, 

 it is probable that there is a common cause for the ending of 

 the series (the casting ofi of the superficial part of the mucosa 

 in both cases). This theory has been further elaborated by 

 Beard, who has arrived at the conclusion that parturition takes 

 place at the time it does in order that a new oxiilation may be 

 carried into effect. This author lays great stress upon the 

 rhythmical character of the sexual processes, and points out 

 in support of his theory that " heat " and ovulation frequently 

 ensue shortly after parturition. That this does not happen in 

 many animals has been aheady shown in the second chapter of 



^ Spiegelberg, " Die Dauer der Geburt," Lehrbuch der Oeburtshillfe, vol. ii. 

 1891. 



^ Tyler Smith, Parturition and the Principles and Practice of Obstetrics, 

 London, 1849. 



' Minot, " Uterus and Embryo," Jour, of Morph., vol. ii., 1889. " Human 

 Embryology." 



' Beard, The Span of Gestation and the Cause of Birth, Jena, 1897. 



