In bilateral cerebellar exposure, however, the patient must be placed on his face, the forehead resting on special supports, and the shoulders on props or pillows so as to allow of free entry of air into the chest. In such cases the anæsthetic is administered from below. I am not enthusiastic over the so-called dental-chair position, but the operating table should be constructed in such a manner that the head and shoulders of the patient can be well raised, the body being inclined to the floor at an angle of about 30-40 degrees. =Preparation of the operative field.= When the patient is fully under the anæsthetic, the final cleansing of the scalp is carried out and the operative field cut off from all possible sources of infection. In the States, in Cushing’s clinic, the anæsthetist is completely covered with a large sterilized sheet, which is fastened to the head of the patient. In this country we prefer that our anæsthetist should have full knowledge of the progress of the operation, and I think that the advantages are with us. In any case, the whole head is enveloped in gauze, two or three layers thick and about 18 inches square. This sheet is thrown over the patient’s head and maintained in position by means of the scalp-tourniquet (see pp. 14, 15). Around this sterilized towels are arranged, either fastened to one another or stitched to the scalp. When the operation is conducted in the temporal region the towels, unless fastened to the skin by means of a few sutures or safety-pins, tend to become displaced, and by so doing add to the risk of wound infection. THE CONTROL OF HÆMORRHAGE =Hæmorrhage from vessels of the scalp.= All surgeons must have appreciated the difficulty attendant on the application of forceps to, and the ligature of, divided scalp-vessels. The patient may lose a considerable quantity of blood, and much valuable time will be wasted before the more essential part of the operation is commenced. All this can, under ordinary circumstances, be avoided by the use of the scalp-tourniquet. As used by Cushing it consists of a rubber ring fashioned after the style of an Esmarch’s tourniquet, encircling the head and passing from the lower frontal region in front, above the ears, to the lower occipital region behind. A median tape, passing from glabella to occiput, prevents any tendency for the tourniquet to slip down over the eyes, at the same time acting as a convenient landmark for the superior longitudinal sinus. The tourniquet, when applied with the correct pressure, should, under ordinary circumstances, completely control all hæmorrhage from the divided scalp-vessels. It should be noted, however, that bleeding will be rather increased than otherwise if the tourniquet be so loosely applied as to impede the venous return without compressing the scalp arteries. A little experience will soon enable the operator to gauge the requisite pressure. [Illustration: FIG. 4. THE SCALP-TOURNIQUET. _Front View._]