648 DK MATTHEWS DUNCAN ON A LOWER LIMIT TO THE 



der Geburt," contained in the first part of the twenty-second volume of the 

 " Monatsschrift fur Geburtskunde" for 1863. This paper anticipates to a very 

 great degree the plans and results here related. But it may be pointed out that 

 Dr Poppel has neglected to note some conditions of the experiment, which cannot 

 be omitted without damaging materially the accuracy and value of the trials ; 

 especially, he has always supposed the membrane to burst when in a hemi- 

 spherical form, which is certainly an error, and one whose tendency is always to 

 make the strength of the membrane too little (vide equation (2) ). He has 

 attached some weight to the part of the amnion tested, considering that greater 

 strength would accompany proximity to the placenta ; but my experiments did 

 not confirm this opinion. 



Dr Poppel's apparatus may be sufficiently, though not fully, described as 

 follows : — The membrane to be tried he ingeniously fixed over one or other of two 

 glass vessels, of the diameter of five centimetres or two inches, and of ten centi- 

 metres or four inches, respectively. The glass vessels were reagent glasses, from 

 which the bottoms were taken off. The affixed membranes represented the 

 bottoms of the reagent glasses. Into the corks of the glasses a long glass tube was 

 passed. Through this tube mercury was poured into the bottle till it filled it, 

 and mounted into the tube. Its height in the tube at the time of the bursting 

 of the membranes was carefully noted, because from it was estimated the pressure 

 that burst the membrane. In adding the mercury fitfully, Dr Poppel erroneously 

 supposed that he imitated the pains of labour, a point, it appears to me, of no 

 importance ; and besides, his idea was manifestly erroneous, for each succeeding 

 pain is not an addition to a force previously in action— it may even be weaker 

 than its predecessor. In every natural case it is an entirely new force, rising in 

 strength from zero to its acme, and again gradually fading to zero. Dr Poppel 

 made allowance for the weight of mercury contained in the reagent glass, over 

 and above what was in the vertical glass-tube ; but he neglected the important 

 element of the degree of bulging of the membrane or radius of its curvature at 

 time of bursting, with a view to arriving at the diameter of the globe, of which 

 it formed a section at the time of rupture. With this he connects also a state- 

 ment, that the bulging of the membranes through the mouth of the womb rarely 

 exceeds a hemispherical form, which, though perhaps nearly true, is misleading, 

 if held to be true in regard to the class of cases of persistent membranes specially 

 studied in this paper. 



The average strength of the amnion found by Poppel was, keeping an aper- 

 ture of 225 inches in radius in view, 19-21 lbs. ; in my experiments it was 

 16-73 lbs. 



Poppel experimented on the membranes in seven cases in which they burst 

 " with the birth." The following table gives the strength of the membranes in 

 these cases, according to Poppel's method of calculating, and the same changed 



