It is composed of three portions: 1. A pelvic arc, a, b, c, d. 2. A_ straight rod, e, f. 2. A canula.
The pelvic arc is terminated at each end by a quadrangular loop, cov ered by rubber, and intended to receive the tuberosities of the ischium. The dimensions of the arc are important. From a to c 3.5 inches, from b to d 4 inches. The width of the loops from a to b and from c to d is 2.7 inches.
The arc is in two pieces, joining and holding firmly the rod at e. The instrument may thus be taken apart, and the arc increased, where the head is large.
The rod of is straight to f, where it bends forward, making an angle at f with the canula gf of 140°.
The canula fg incloses a rod which is moved by turning the transverse handle, and this rod imparts motion to t. It is to t that the loops of the rods of the forceps, or the lower sling of the sericeps, are attached. At the beginning of labor t is at f, at the end of labor t is at g.
At o each blade of the forceps is pierced for the passage of the traction chains, which are thus inserted (and this is important) at the level of the centre of the foetal head. • This tractor rests on the pelvis, in front, and behind each tuberosity. These four points, a, b, c, d, form a quadrangle through which pass the traction cords. The instrument holds the position given it, each turn of the handle simply applying it closer against the pelvis.
The operator may dispense with an assistant, and he may manipulate the instrument with one hand, while the other sustains the perineum. He is further able to alter the axis of the tractor at will; thus, at the be ginning of labor, as far back as possible, in the middle of labor, as far forward as possible. The instrument makes, at first, traction backward, perpendicularly about to the inlet, and later tractions forward, perpen dicularly to the inferior strait. Figure 67 shows the tractor pulling the forceps, the head at the superior strait. The dotted lines show the posi tion of the instrument at the end of labor.
My colleague, Bailly, has brought forward the following objections against the use of mechanical tractors in labor: 1. These tractors substitute blind force for that of the sentient guiding band.
2. They act in only one direction, and do not allow us to change the traction line according to the change in the pelvic axis; consequently ob lique force is applied to the pelvic walls, which, from mechanical princi ples, results in loss of direct force.
3. Mechanical tractors interfere with lateral movements of the forceps.
4. They may slip from the head before the accoucheur knows it; and, if a force of 17 to 18 pounds is being exerted, what may not happen to the maternal parts? 5. If manual traction be sufficient to bring down the head through a contracted pelvis, whenever this is at all possible, what scope or necessity is there for mechanical tractions? 6. The time requisite for the introduction of these instruments must add to.the maternal suffering.
7. Facts have proved that not only are mechanical tractions dangerous for the mother, but that further the very foetal lesions which they aim to prevent are more frequent than after the use of the ordinary forceps.
Although the modifications of Pros and of Poullet have negatived cer tain of the above objections, the others are still valid, and we are in per feet accord with Bailly, Depaul and Pajot, who absolutely reject mechani cal tractors. Tarnier is less positive, and he believes that, in the future, all these objections against mechanical tractors will be overcome.
Starting with the assumption that manual traction varies with the mus cular force of each individual, and from moment to moment, he proves that mechanical traction is, on the contrary, progressive, and may fur thermore be limited and gauged by means of the dynamometer, and this latter adjunct is indispensable.
The principal objection, in his opinion, resides in the constant action of mechanical tractors. He has endeavored to overcome this as follows: " Through the fenestra) of an ordinary forceps he passes a double sling, the ends of which are tied together externally, and looped over a dyna mometer. ( Vide Figs. 68, 69 and 70.) This dynamometer is connected with a fixed point, a hook in the floor, six feet distant.