POWER EXERTED IN THE FUNCTION OF PARTURITION. 641 



acted in a fair and satisfactory manner was evident, from the observation that, 

 in almost all the trials, the membrane tested did not burst where it touched the 

 instrument, but in an arc of a circle crossing over the bulged out membrane ; or, 

 rarely, in a starlike manner. Connected, by a hollow arm, with the apparatus 

 was a vertical tube g, with scale /of inches and tenths of inches. This tube con- 

 tained a long column of air, confined in it by a short column of mercury. The 

 rise of the column of mercury compressing the air in the tube indicated the 

 degree of pressure applied to the internal surface of the membrane fixed over the 

 mouth of the conical vessel d. Besides my own supply, I was kindly pro- 

 vided with fresh membranes by Dr Linton and Mr Vachee. 



The following table gives, in a categorical form, a narration of each of 100 ex- 

 periments, as well as the chief calculations founded upon the data obtained from 

 them. The first column gives the number of the trial. The second column gives 

 the number of the set of membranes tested ; and it will be seen that generally 

 several experiments were made with the same membranes. The third gives the 

 length of continuance of labour till the time when the membranes were ruptured. 

 The fourth column gives the duration of the first stage of labour. The fifth 

 gives the duration of the second stage of labour. The sixth column contains 

 the state of the os uteri at the time of the rupture of the membranes. The seventh 

 states the stage of labour in which the bag of waters was broken. The eighth, 

 ninth, and tenth columns show how many of the three membranes were tested 

 simultaneouslv. The eleventh, twelfth, and thirteenth columns show what 



J 7-7 



membranes gave way in each experiment. The fourteenth column states the 

 radius of the circular mouth of the apparatus to which the membranes were tied. 

 The fifteenth gives the barometric pressure at the time of each trial ; and it will 

 be observed that the pressure occasionally required a correction which demands 

 explanation. The column of mercury in the apparatus was generally very short, 

 and no correction for its weight was required, the experiments not pretending to 

 an extreme nicety; but occasionally (in the cases noted in the column of re- 

 marks) the column of mercury was too long to be neglected, and a correction 

 was made for its length. The sixteenth column gives the length of the column 

 of air enclosed in the vertical tube above the mercury. The seventeenth gives 

 the contraction of this column of air, by the pressure of water which burst the 

 membranes, acting on the short column of mercury. The eighteenth column gives 

 the height of the membrane as it bulged above the mouth of the apparatus, ex- 

 panded by the water pressure. The nineteenth gives the effective pressure of 

 the water, at the moment of bursting of the membrane, in inches of mercury. 

 The twentieth gives the diameter of the sphere, of which the membrane when 

 bursting approximately formed a portion. The twenty-first column gives the 

 pressure per square inch of the membrane at the time of the bursting of the 

 membrane, or at the time of the experiment's failing from some cause, such as 



