The Coagulation Time of the Blood in Man 307 



a pair of fine pliers, until it is found that a smooth and continuous flow is 

 produced by a low pressure of oil. 



The nozzle should then be plastered round with solder to preserve it, 

 for the slightest knock may alter it a little, and unless it is exactly right 

 the flow of the corpuscles is rendered jerky and inconstant. 



When the stop-cock is open the box is of course filled with oil, and tbe 

 jet from the nozzJe produces a current which streams across the edge of the 

 drop of blood which is surrounded by oil on all sides except where it is in 

 contact with the end of the cone. When everything is in position the box 

 lies on the stage of a microscope, and tbe flow of the corpuscles can be ob- 

 served with a low-power lens. The oil runs out of the box through a hole 

 in the metal fitting of the cone and foi-ms a pool on the top in which the 

 lens lies when it is in focus. 



The oil is allowed to run over the stage of the microscope and falls into 

 a vessel hung beneath it, from which it is collected by a pipe which conveys 

 it over the edge of the table into a receptacle on the floor. 



An arrangement is also necessary for keeping the oil which surrounds 

 the blood at a constant temperature. The water in the tank is warmed 

 by a small gas-jet which is regulated by S chafer's thermostat. 



This tank is round, is 7 inches high, and has a diameter of 7 inches. 

 It has a dome-shaped bottom so as to raise it some distance above the gas- 

 flame, and is placed on a metal ring 3 inches high which is pierced by holes 

 fo the inlet of air to the flame. 



The oil in the 4^ feet of metal tubing which is immersed in the water 

 soon acquires the same constant temperature. 



A finely graduated thermometer (fig. 2, T) pierces the box into which 

 the cone fits, so that thotigh the shaft is outside, the bulb lies in the 

 interior very close to the suspended drop of blood. In this way, the 

 temperature of the oil immediately surrounding the blood is accurately 

 known. By means of this arrangement the temperature of the oil in which 

 the blood lies can be kept constant at any desired temperature for any 

 length of time. 



The pressure of the flx3>w depends on the height of the level of the oil in 

 the reservoir, and on the calibre of the nozzle. 



With the calibre of nozzle which is at present used by me, the surface 

 of oil must be 10 cm. above the blood. 



The pressure may vary from the obstruction of the nozzle by dust, etc. 

 To obviate this, the oil is twice filtered, before it is introduced into the 

 reservoir. 



It is necessary to have a standard by which the pressure can be gauged. 

 This is most simply attained by measuring the length of the jet of oil when 

 the box is removed. 



When the receiving vessel, which is hung below the stage of the micro- 

 scope, is 39 cm. from the end of the nozzle, the jet of oil just falls into it. 

 If it does not do this, there must be something wrong. The nozzle can then 

 VOL. I., NO. 1 — 1908 21 



