MECHANICAL EXTRACTION OF THE FCETUS. 525 



should be equally applied to every part of the bony girdle in contact with 

 the head of the foetus. But this does not take place with the ordinary 

 forceps, which, even in the hands of the most expert accoucheur, not only 

 acts as a traction agent, but at a given moment is unfortunately trans- 

 formed into a lever of the first or second kind, whose power is incalcula- 

 ble, and which, resting on two opposite points of the pelvic circumference, 

 may burst it, without the dynamometer showing any thing more than a 

 relatively feeble degree of traction. 



Otherwise, it is not only the bones which have to be considered, but 

 also the soft parts, which, pressed between the foetal head and the hard 

 pelvic circumference, may be bruised, contused, or lacerated to a variable 

 degree, if the comparison exceeds a certain limit. This pressure, how- 

 ever, is always considerable ; for, according to Chassagny, when a trac- 

 tile force of fifty kilogrammes is exercised on the head of a foetus seized 

 by the ordinary forceps, we may calculate that each square centimetre of 

 surface of the pelvic walls sustains a pressure of 1800 grammes, even in 

 the most favorable conditions ; though it may be as much as six kilo- 

 grammes or more, according to circumstances. 



These observations, though doubtless valuable and significant for the ac- 

 coucheur of woman, are only very indirectly applicable to veterinary ob- 

 stetricy. Without taking into account the strength of the pelvic osseous 

 girdle, which is so much greater in the Mare and Cow than in woman, 

 several other circumstances allow us to understand why this bony circle 

 may, in these animals, resist an amount of strain which would appear to 

 be altogether unreasonable, if judged according to the principles which 

 should guide the practice of the human obstetrist. But the veterinarian 

 is in possession of means of traction which give him a great advantage 

 in this respect — an advantage which the accoucheur has not yet been 

 able to avail himself of : we allude to the cords the former so frequently 

 employs as traction instruments, and which can never be transformed into 

 levers, like the forceps. 



In woman, as with animals, the foetus, in passing through the pelvic 

 cavity, is pressed upon by its walls, and in return 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 com- 

 pressible 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. Besides all this, 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 centi- ^ 

 metres, 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 favorable cir- 

 cumstances 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 favorable conditions it may 

 even be much more. 



