H 3 8 REPRODUCTION 



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 

 periodical contractions when its bloodvessels are perfused with such 

 an artificial fluid as Locke's solution, or, indeed, when it is simply 

 immersed in the oxygenated solution (Kurdinowski) (Practical 

 Exercises, p. 1147). 



It is a question of great interest how the uterine contractions are 

 started so abruptly at full term after so long a period of quiescence. 

 It can hardly be that the increasing mechanical distension of the 

 uterus, tolerated for so many months, should suddenly, in an hour, 

 become intolerable. For if the foetus dies before full term it is 

 expelled without reference to the bulk which the uterus has reached. 

 It is more likely that some chemical change associated with the 

 completion of intra- uterine development, a change which leads, 

 perhaps, to the production of some specific substance in the placenta 

 or the foetus, is the determining event. The placenta is a structure 

 whose function is strictly limited to the term of intra-uterine develop- 

 ment. The foetus is to live on, and so is the mother. May it not 

 be that the placenta or essential elements in it are timed to die, or 

 to begin to die, at full term, and that in their death or degeneration 

 the substance or substances are produced which start, and later 

 sustain, the uterine contractions ? And may not the contractions of 

 the uterus, by exciting its afferent nerves, or through the pressure 

 of the foetus the afferent nerves of the vagina, in turn evoke the 

 associated reflex contractions of the abdominal walls ? These are 

 questions which have been asked, but not as yet satisfactorily 

 answered. It has also been suggested that a hormone formed in the 

 mammary gland at full term stimulates the uterus and thus brings 

 on labour. 



At birth, great changes take place in the foetal circulation, and these 

 are intimately connected with the commencement of the respiratory 

 activity of the lungs. The causes of the first respiration are: (i) The 

 increasing venosity of the blood circulating in the bulb, which stimu- 

 lates the respiratory centre when the umbilical cord has been cut o: 

 tied and the placental circulation thus interfered with ; (2) the stimula- 

 tion of the skin by the air, which, as we have seen, acts reflexly upon the 

 respiratory centre. That both of these factors may be involved is 

 shown by the fact that either compression of the umbilical cord alone, 

 or exposure of the foetus by opening the uterus of an animal without 

 interference with the circulation, has been observed to be followed 

 by attempts at breathing. Once distended, the lungs never again 

 completely collapse not even after death, nor when the chest is 

 opened. The aspiration caused by the elevation of the chest- walls in 



