1877.] 



Action of the Sphincter Ani. 



79 



was seen, for instance, when the wooden head of the instrument was 

 pressed down upon the sphincter. The most ready way in which the 

 effect was produced was by making the patient cough. This initial con- 

 traction was also very marked on the irritation produced by the intro- 

 duction of the instrument, the invariable effect being the succession of 

 changes of pressure which are shown in the tracing (fig. 2). The vertical 

 rise (a) is the effect of the pressure of the sphincter to which the instru- 

 ment is suddenly exposed on its introduction ; the top of this line repre- 

 sents the amount of pressure exerted by the sphincter before the 

 introduction of the instrument. This is followed by a slight rise (6), 

 succeeded by a considerable and rather quick fall (c), which fall is again 

 succeeded by a rise (d) to a point a little higher than that from which 

 the lever fell, as in the effect of the injection of air. 



In the slow rise after this inhibition there was often an indication of 

 a tendency to rhythmical action. In some tracings, especially those 

 which show the effect of a cough, this is very distinct (fig. 3). The 

 slight fall (b) immediately after the cough is the result of the movement of 

 the instrument lessening the extent to which it is compressed by the 



