Anatomy of the Umbilical Cord, 435 



verse sections of the umbilical arteries, distended and undistended, with 

 vegetable-colour stains. 



I have already stated that I have failed to find any trace of nerve- 

 fibres in any part of the cord. By what mechanism, then, can this 

 process of contraction be set going ? It seems to me that the answer is 

 readily found in three facts. First, there is no endothelium in the 

 umbilical arteries, and the muscular fibres are therefore directly in con- 

 tact with the blood which flows in them, that blood being venous as long 

 as the placental circulation continues *. Second, it has now been well 

 established, by Dr. BAckard Norris and others, that contractility exists 

 in muscle itself, and "that nerve-influence is only its regulator, its exciter, 

 or even its controller. Muscles depend most for their contractility on 

 the contact of arterial blood. Thirdly, in the infant this happens to the 

 muscular fibre of the umbilical arteries with the first few respirations. 

 The blood in them up till that time has been venous, and suddenly 

 becoming arterial, it throws them into violent contraction. By the ces- 

 sation of the supply of arterial blood they may again dilate; for Simpson, 

 in his collected memoirs (posthumous edition, vol. i. p. 228), says, " It is 

 generally acknowledged by physiologists, as the result of various observa- 

 tions, that immediately after the child is born the umbilical vessels cease 

 to pulsate and carry blood if the pulmonary respiration becomes active, 

 and if the pulmonary respiration is by any cause interrupted or arrested 

 before the cord is divided, the circulation through the umbilical vessels 

 again becomes more or less active. Hence various practitioners have 

 gone so far as to aver that it is unnecessary, as a general rule, to place 

 a ligature upon the foetal extremity of the cut umbilical cord if the cord 

 be not cut till the child has cried loudly." 



This I have repeatedly verified by experiment. By refraining from 

 dividing the cord for a few minutes after the child is born, some very 

 interesting observations can be made. If the child do not cry at once, 

 and the placenta be left in situ, the arteries of the cord may be felt to 

 pulsate strongly. If the child cries freely, they at once cease to beat and 

 contract to firm threads, being felt through the flabby cord almost like 

 cartilage. Should the child's respiration cease for a few moments they 

 again relax and pulsate, and contract once more when the child cries. 

 "When the possibility of the circulation through the cord is arrested by 

 the application of a ligature its stump soon ceases to give any indication 

 of pulsation, because only arterial blood can then pass into it. The con- 

 traction and subsequent obliteration of the hypogastric arteries take place 



* The arterialization of the blood in the capillaries, especially of the central veins 

 of the cord, may also have much to do in exciting the contraction of the arterial coats. 

 It may also be from this central sinus that this peculiar form of haemorrhage occurs, 

 which is sometimes seen after the separation of the stump. 



This haemorrhage is passive but arterial, and is seldom controlled by any ordinary 

 haemostatic agency. The absence of muscular walls from this sinus seems to explain 

 some of the facts of this haemorrhage, 



