526 OBSTETRICAL OPERATIONS. 



cavity is pressed upon by its walls, and in turn it presses upon them, 

 in the manner of a wedge which tends to tear them asunder. But there 

 is a great difference in woman and animals. On the one hand, it is a 

 hard, bony, and little reducible region — the head — which presses against 

 the pelvic walls, to which it transmits, almost undiminished, the pressure 

 itself receives ; on the other hand, it is a bony cage — the chest — formed 

 of numerous very movable parts, and which can submit without injury 

 to much distortion, in addition to its being covered by soft and readily 

 compressible tissues ; consequently, we can easily comprehend how much 

 in the latter case — that of animals — the eccentric pressure produced by 

 the passage of the foetus should be attenuated. In addition, the head 

 of the infant is spherical, and therefore comes in contact with the interior 

 of the mother's pelvis by a circle or narrow zone ; the surface of the 

 pelvis in contact with the foetal head has been estimated at sixty square 

 centimetres, and it is to this limited space that the head transmits the 

 pressure it sustains. Chassagny, from a series of experiments, estimates 

 that, for a traction of sixty kilogrammes — exerted under the most favour- 

 able circumstances by his forceps on the head of the human foetus — each 

 square centimetre of the surface of the pelvis in contact with it should 

 support a pressure of about 500 grammes ; in less favourable conditions 

 it may even be much more. 



From some measurements made by Saint-Cyr, the pelvis of the Mare 

 and Cow, which is nearly cylindrical, may be reckoned at 1,600 square 

 centimetres (248 inches) of internal surface ; and it is on this expanse 

 that is distributed, in a nearly uniform manner, the eccentric pressure 

 which the chest of the foetus transmits to the walls of the genital canal, 

 to which it is very closely applied during its passage outwards. If, then, 

 it be admitted that the total of this eccentric pressure amount to about 

 one-half the tractile force expended on the foetus, it will be easy to find, 

 by a simple calculation, the pressure on each square inch. Supposing 

 the traction to be equal to 1,540 pounds — the estimated strength of 

 seven or eight men pulling with all their force at the cords — the 

 pressure on each square inch would be about 7f ounces ; or one-half that 

 exerted on the same extent of surface with a tractile force of 132 pounds, 

 in woman ! 



Saint-Cyr does not pretend that these calculations give a rigorously 

 exact measure of what really takes place during parturition ; but he 

 believes they may assist, up to a certain point, in explaining certain facts 

 in comparative obstetrics which otherwise would remain obscure — how, 

 for instance, natural birth, which is always so painful in woman, 

 is comparatively painless in the lai'ger animals ; and why traction, 

 the very idea of which alarms the accoucheur of woman, is in the 

 majority of instances so well sustained by the veterinary surgeon's 

 patients. 



It must be confessed, however, that we have as yet no certain data by 

 which we can estimate the exact amount of force necessary, or which 

 may be employed without danger; and on this point the opinions of the 

 best authorities are widely divergent. Some declare for moderate 

 traction — tv>'o, three, or four men at the most, pulling simultaneously 

 at the cords with all their force, are, in their opinion, quite sufficient in 

 all cases, if well managed ; and they assert that it is rash and dangerous 

 to employ more. Others do not hesitate to have recourse to more 

 energetic traction, and are not afraid of employing the combined strength 

 of six, eight, or ten strong men ; being convinced that the parent suffers 



