544 THE PHYSIOLOGY OF REPRODUCTION 



(11) Lastly, WilKams calls attention to the fact that ex- 

 cessive physical fatigue, sudden jars or violence, mental emotion, 

 fright, &c., may lead to the termination of gestation in women. 

 Similarly, it is well known that circumstances of a like nature 

 may induce abortion in animals. 



Williams remarks that in all probabihty the onset of labour 

 in most cases is due to a combination of a number of the 

 above-mentioned causes. The main objection to aU the 

 theories which have so far been advanced is that they take no 

 account of the complexity of the problem. An hypothesis may 

 be fairly adequate as a general explanation of the duration of 

 gestation, while at the same time taking no account of the 

 immediate cause of birth. Thus, it is no doubt true that the 

 time of parturition is determined largely by the necessities 

 of the offspring, but this conclusion provides no sort of ex- 

 planation as to why it is that the pains of labour in any one 

 particular species generally commence at a certain fixed stage 

 of development, and it remains for us to assume that it is one 

 of the inherent properties of the uterus in the species in question 

 that they should do so. Even on this assumption it is im- 

 possible to avoid concluding that there must be some definite 

 exciting cause, such as that postulated by Spiegelberg. 



Prolonged Gestation 



The duration of gestation in any one species usually varies 

 within quite narrow hmits, but under exceptional circumstances 

 it may continue for an abnormally long period. Thus, WiUiams ^ 

 records a case of a woman with whom pregnancy extended for 

 over eleven lunar months after the cessation of menstruation, 

 instead of the usual ten lunar months {i.e. about 280 days). In 

 this case typical labour pains were experienced at the end of 

 the tenth month, but these subsided after a short time, and 

 were not renewed until four weeks later, when they resulted in 

 parturition. The same woman became pregnant a second time, 

 when the period of pregnancy was again prolonged until the 

 end of the eleventh month after the last menstruation. The 

 children on each occasion were abnormally large and heavy 



^ Williams, loc. cit. 



