By drawing the cannulas from a single piece of glass tubing and by making the distance from shoulder to upper end about twelve millimeters, receptacles of fairly uniform capacity are assured. All the dimensions, the reach of the rubber connection over the top of the cannula (2-3 millimeters), the distance of the upper rubber ring from the lower end of the glass chamber (4 centimeters), etc., were as nearly standard as possible. A copper wire _D_, eight centimeters long and 0.6 millimeters in diameter, bent above into a hook and below into a small ring slightly less than two millimeters in diameter, is hung in a depression at the end of the short arm of the lever. The small ring then rests in the upper part of the cannula (see Fig. 24). The weight of the copper wire makes the short arm of the lever heavier than the long arm by 30 milligrams, when the delicate writing point is moving over a lightly smoked drum. Half a dozen of these standard wires are needed. For accurate determination of the coagulation time Addis[100] has defined the following conditions as essential: 1. The blood must always be obtained under the same conditions. 2. Estimates must all be made at the same temperature. 3. The blood must always come in contact with the same amount and kind of foreign material. 4. The end point must be clear and definite and must always indicate the same degree of coagulation. The precautions taken to fulfill these conditions were as follows: 1. _Drawing the blood._--The blood was taken from the femoral artery. The artery (usually the right) was laid bare in the groin and freed from surrounding tissue. A narrow artery clip, with each limb enclosed in soft rubber tubing (to prevent injury of the tissues), and with its spring exerting gentle pressure, was placed on the artery immediately below the deep femoral branch, thus allowing no blood to stagnate above the clip. Between the clip and a ligature applied about 1.5 centimeters below, an opening was made. The blood was carefully milked out of the vessels between a blunt dissector moved beneath, and a small forceps, twisted into a pinch of absorbent cotton, moved above.