REPRODUCTION 1019 



like the respiratory, vaso-motor, and cardio-inhibitory. Even when 

 totally deprived of oxygen, as by pressure on the umbilical cord 

 during delivery, the child does not perish in the two or three minutes 

 which decide the fate of the asphyxiated adult ; nor are the con- 

 vulsions, rise of blood-pressure, and slowing of the heart-beat, 

 associated with asphyxia in the latter, so readily induced, nor 

 premature and fatal efforts at respiration easily excited in utero. 

 But although - in such a case the embryo behaves as a separate 

 organism, governed by i^s own laws, there are circumstances in 

 which it becomes merely a part of the mother and participates in her 

 fate. Thus, the stream of oxygen which normally passes from the 

 maternal to the foetal blood is turned back if asphyxia threatens 

 the mother; the blood of the umbilical arteries, instead of being 

 purified in the placenta, loses the little oxygen it holds to the 

 blood of the uterine sinuses, and the tissues of the embryo are 

 impoverished to support the metabolism of the maternal organs. 

 In the same way, the phenomena of starvation have taught us 

 that the nutrition of the organism is not subject to the rules of 

 red tape. In normal circumstances the flow of nutriment follows 

 definite lines : the blood feeds the tissues through its intermediary, 

 the lymph, and recoups itself from the contents of the alimentary 

 canal. But when the normal sources of nutrient material fail, the 

 body falls back upon its stores. The organs immediately necessary 

 to life are kept, as far as possible, on full diet ; organs of secondary 

 importance have to be content with half-rations ; organs less im- 

 portant still are drawn upon for supplies. 



Parturition. The period of gestation is abruptly closed about 

 280 days after the last menstruation, usually in what would have been 

 the tenth intermenstrual period had menstruation been occurring. 

 There is necessarily a considerable variation in the time when 

 reckoned in this way, since the cessation of the menses merely an- 

 nounces that conception has occurred some time after the last 

 period. It may even be disputed whether the fertilized ovum 

 corresponds to the last menstruation or to the first absent 

 period. Parturition, or the .expulsion of the foetus, is accom- 

 plished by periodical contractions, the ' pains ' of labour, at first 

 confined to the uterus. Soon the os uteri begins to soften and 

 dilate, the walls of the vagina become congested, and its secretions 

 are augmented. The uterine contractions increase in frequency 

 and force, and are now accompanied by reflex contractions of the 

 abdominal muscles, and, if the woman is not anaesthetized, also by 

 voluntary contractions of these and of other muscles, which can 

 increase the intra-abdominal pressure. The uterine contractions 

 can be initiated and modified by impulses coming from the central 

 nervous system by way of the extrinsic nerves of the organ. It is 

 known, e.g., that the gravid uterus can be excited to contraction by 

 the stimulation of various sensory nerves. Powerful mental impres- 

 sions, such as fright, may bring on premature labour. Conversely, 

 sudden cessation of labour pains during parturition is not uncom- 

 monly observed to be produced by emotional disturbances for 

 instance, the entrance of a stranger into the room. Yet the con- 

 tractions of the uterus are not essentially dependent upon extrinsic 

 impulses. For not only do rhythmical contractions occur, but the 

 whole process of parturition has been seen to take place in a uterus 

 whose nerves have all been cut. Even the excised uterus may be 

 kept alive for as long as forty-eight hours, and may go on executing 



