427 
1888.] Prof. Tait on Theory of Internal Pressure. 
Hence the work above spoken of is 72 inch-tons. 
But to evaporate a cubic inch of water at 0° we require 
606. 1390 foot-lbs., 
172o 
or 163 inch-tons, 
more than double. 
In the former case, however, it is water which comes out ; in the 
latter, steam. 
PRIVATE BUSINESS. 
Mr W. Ivison Macadam and Mr James Oliphant were balloted 
for, and declared duly elected Fellows of the Society. 
Monday, Wi July 1888, 
Sir DOUGLAS MACLAGAM, Vice-President, in the 
Chair. 
The following Communications v/ere read 
1. The Mechanism of the Separation of the Placenta and 
Membranes during Labour. By D. Berry Hart, M.D., 
F.R.C.P.E., Lecturer on Midwifery, Surgeond Hall, Edinburgh. 
(Plates XVIII., XIX.) 
During labour the membranes and placenta become separated and 
expelled, but while the expulsion of these takes place after the child 
is born, the entire separation does not occur at any one period. 
During the first stage of labour the membranes in the lower 
portion of the uterus, in the part termed the lower uterine segment, 
become detached. The placenta, if placed partly in this segment, 
a condition known as placenta praevia, becomes also separated. 
The rest of the membranes and placenta do not become separated 
until after childbirth, and this is followed by their expulsion as a 
whole. 
The question to be considered at present is this : How are the 
membranes and placenta separated*? Is the mechanism in all of them 
the same, or Have we one for the separation of the part of the 
membranes and placenta when in the lower uterine segment, and 
another for the portions attached higher up ^ 
