894 REPRODUCTION, DEVELOPMENT, GROWTH AND DEATH [CH. LIX. 



exterior. The process usually lasts some hours, bufc the time is much 

 prolonged (ten, twenty, or even more hours) in the birth of a first 

 child. The child is still connected with the placenta by the umbilical 

 cord, which is about 20 inches long, and this connection should not 

 be severed for a few minutes in order that as much blood as possible 

 may be aspirated from the foetal part of the placenta into the child 

 as breathing commences. 



After the child is expelled, the contractions of the uterine walls 

 recommence after a lapse of twenty to thirty minutes, and the 

 placenta is separated and forced out. The separation extends 

 through the decidua along the line of the stratum spongiosum, and 

 the fused chorion, amnion and decidua turned inside out, follow the 

 placenta to which they are attached, constituting, with the placenta, 

 the after-birth. 



After the umbilical cord is tied and separated, the umbilical 

 arteries inside the child become filled with blood-clot, and ultimately 

 they are converted into fibrous cords, the so-called obliterated hypo- 

 gastric arteries, and at the same time the allantois is also converted 

 into a fibrous strand, the urachus, which extends from the apex of the 

 bladder to the umbilicus. 



The haemorrhage from the uterus which accompanies and follows 

 the after-birth may be profuse at first, but under normal circum- 

 stances is soon checked by the firm contraction of the uterine 

 walls. 



Although it has been shown that delivery may occur when all nerves connect- 

 ing the uterus with the central nervous system are cut through (see p. 721), the 

 contractions of the organ are normally influenced reflexly through the nervous 

 system. Stimulation of various sensory nerves will produce contractions of the 

 pregnant uterus, and premature delivery may occur as the result of mental and 

 physical disturbances. 



The determining factor which produces the labour pains at a particular date 

 has been much discussed; some suppose it may be maternal in origin, such as 

 a degenerative condition set up in the placenta or decidua, whereas others consider 

 the initial impulse may come from the foetus, which secretes certain products that 

 stimulate uterine contraction. 



After delivery, the uterus undergoes reduction in size at a fairly 

 rapid rate. This has been attributed to fatty degeneration, but of 

 this there is but little evidence. The theory at present most in 

 vogue to explain " involution of the uterus " is that the process is 

 one of autolysis due to the action of intracellular digestive enzymes. 

 Whilst it is occurring, the urine of the mother contains a good deal 

 of creatine, a substance which is normally absent from that secretion. 

 It has been supposed tha-t this* 'substance originates from the rapid 

 destruction of the- uterine /muscte. - It has, however, been shown that 

 creatine occurs aftef ' delivery even if the uterus is amputated, so 

 that the muscular creatine cannot then be the source of the urinary 



