164 Proceedings of the Royal Society 
It was interesting to point out that although the patient and a 
skilled observer might not remark any increased strength of labour 
as it advanced, yet. in consequence of the diminished dimensions 
of the uterine cavity, its muscular action, though the same, had 
greater effect or power. 
Dr J. Poppel had made similar experiments, which anticipated 
some of the results of this paper. But his method of experiment- 
ing was open to the grave objection, that he always supposed the 
membrane to burst when in a hemispherical form — an error whose 
tendency is to make the strength of the membrane too little, and 
which may account for the difference between his results and those 
given in this paper. 
Poppel experimented on the membranes of seven cases in which 
they burst “ with the birth.” In these cases, according to Poppel’s 
method of calculating, and changing his results only so far as to 
make them comparable to those of this paper, the power terminat- 
ing labour varied from about 6 to about 27 lbs. 
The interesting result is thus arrived at, that in some of the 
easiest cases of labour the mere weight of the child, if duly applied, 
gives a force sufficient to effect delivery. 
The average strength of the amnion found by Poppel, keeping 
in view an aperture of 2*5 inches in radius, was about 19 lbs. ; by 
Dr Duncan, about 17 lbs. 
Dr Duncan proceeded to show how an estimate could be formed 
of the force exerted in the most difficult labours spontaneously 
terminated. Joulin had stated it as about 100 lbs., while Dr 
Duncan believed it did not exceed 80 lbs. 
Dr Duncan then observed that he knew of no method of ascer- 
taining the powers of ordinary labours. But he described, though 
he did not recommend the use of, means by which it could be 
ascertained in any case. The essential part of this was the dis- 
covery of the pressure to which the pool of liquor amnii retained 
in utero after the rupture of the membranes was subjected as the 
labour progressed. 
