1888.] Dr Berry Hart on Separation of the Placenta. 433 
fact has an increase in area in its anterior and posterior surfaces. 
Now comes in a different phase in the behaviour of the placenta. 
The foetal blood has been aspirated from it ; the intervillous spaces 
are empty, and therefore during the increase in the internal 
uterine area, we have cut off the two factors in bringing about the 
equivalent expansion in area of the placenta during the relaxation 
following the pains of the first and second stages ; i.e., we get the 
placenta smaller in area at the plane of separation than the 
placental site. This repeated disproportion in area, ^.e., slight excess 
of area of the placental site over that of the placenta itself, tears the 
trabeculae in the spongy layer, i.e., separates the placenta. This 
disproportion need only be slight, as we know how early the placenta 
when prsevia begins to be separated over the expanding lower 
uterine segment. During the third stage separation, blood may be 
effused by the relaxing muscle, and collect between uterine wall 
and placenta. The retroplacental clot or blood effusion is a con- 
sequence of the separation, and relieves the maternal system of 
some blood that might embarrass the heart’s action when aspirated 
to the right side. 
The last phenomenon in the third stage is the expulsion of the 
separated placenta, when it either comes edge-ways or inverted. 
This mechanism of Duncan and Schultze has nothing to do with 
separation, but belongs to expulsion. 
The placenta during the third stage of labour is therefore 
separated after the pain dies off, when the trabeculae of the spongy 
layer are torn, owing to the increase in the placental site not being 
participated in by the placenta itself. We thus get the disproportion 
of separation which is necessary to tear these trabeculae. 
The membranes are separated during the third stage in entirely 
the same way. The wrinkled and folded membranes lying above 
the spongy layer do not participate in the increase in area of their 
site after a pain, and the tension thus put on their trabeculae tears 
these, and thus separates them. 
All the separation of membranes and placenta occurring in nor- 
mal or abnormal labour can thus be accounted for in one way. 
Separation of placenta and membranes takes place owing to a dispro- 
portion between the part to be separated and the site of its attachment. 
Below the contraction ring, the increase in site is brought about 
