LABOR PAINS 61 



influences may also cause uterine contraction, which will be 

 discussed fully under "Abortion." 



As a result of uterine contraction the placental circulation 

 is lessened and a small amount of blood enters the placenta. 

 During the labor pains the foetal heart-beats become slower. 

 One looks upon this as an excess of carbon dioxide in the foetal 

 blood. The increasing frequency of the maternal heart-beat 

 during labor pains causes a rise of pressure in the arterial 

 system — a compensation, to a certain extent, for the limited 

 amount of blood following narrowing of the arterial channels 

 (Kehrer). The contractions of the uterus are not of a peris- 

 taltic nature, as the whole contractile surface acts together. 

 The pressure following labor pains is considerable. 



Poullet ascertained the intensity of labor pains mano- 

 metrically by an apparatus termed by him " Tocograph." 

 This instrument transfers the pressure, the result of the 

 uterine contraction during labor pains, to a manometer, which 

 records it upon a rotating roll of paper— that is, in the same 

 manner as we produce pulse and respiratory curves. The 

 apparatus of Poullet consists of, first, a strong but compres- 

 sible caoutchouc ball; the ball is introduced into the uterus, 

 between its walls and the foetal envelopes, when the latter are 

 torn between the uterine walls and body of the foetus. Second, 

 it consists of a mercury manometer, a U-shaped tube, partly 

 filled with mercury, and one arm of which communicates with 

 the ball by means of a caoutchouc tube, while the other arm 

 has a float, the end of which is provided with a pen to 

 register the movements of the mercury. When the apparatus 

 is started without introducing the caoutchouc ball into the 

 uterus, the pen records upon the rotating paper a horizontal 

 line, termed zero. On introducing the ball in the proper 

 manner into the uterus during labor pains, and connecting it 

 with the apparatus, the water in the ball becomes compressed 

 and the pressure is transferred to the mercury, causing it to 

 rise in that arm of the U tube with which the ball is con- 

 nected. During the intermission the mercury falls, registering 

 a horizontal line. Each intermission produces the same hori- 



