of Edinburgh , Session 1866-67. 
163 
5 Oil a Lower Limit to tlie Power exerted in the Func- 
tion of Parturition. By J. Matthews Duncan, M.D. 
In this paper the author’s object was to show what propelling 
power was required and produced to push the foetus through the 
passages into the world in the easiest deliveries. The fact chiefly 
founded on, as affording a basis for the necessary calculations, was 
the occasional birth of the ovum entire, that is, the membranes 
containing the foetus and liquor amnii being entire after passing 
through the maternal passages. In such cases the strength of the 
amniotic membrane was greater than that of the parturient or ex- 
pulsive power. The expulsive power was in them never so strong 
as to break the bag of membranes ; and the tensile strength of the 
membrane being ascertained by experiment, the propelling power 
could be calculated from it. 
In like manner, in labours in which the expulsive efforts merely 
ruptured the bag in the last pains, or did not increase in power 
after the rupture, the tensile strength of the membranes afforded, 
along with other data, the means of estimating with considerable 
certainty and exactness the effective force which completed the 
labour. 
One hundred experiments were performed upon the foetal mem- 
branes in many different cases, in order to acquire data for the 
calculations above referred to. In conducting them, Dr Duncan 
had the assistance of Professor Tait, who also pointed out the 
method of making the computations from the data acquired in 
them. 
After experimentally ascertaining the tensile strength of the 
membranes, the power of the labour at the time of the rupture of 
the bag was found, and it was held that the lumen of the passage 
opened up by the advancing ovum was circular, and of 4|- inches, 
in diameter, and that the bulge of the unsupported membrane was 
hemispherical. The force required to rupture the weakest amnion 
showed that the power of the labour was at least 4*08 lbs., that for 
the strongest 37 - 58 lbs. ; and the average power indicated by the 
experiments on the amnion was 16 - 7?> lbs. 
