The Coagulation Time of the Blood in Man 309 



temperature of the oil is 70° C. or more. After they have been left in for 

 a few minutes they are fitted into the necks of small bottles containing 

 ether. The bottles are then well shaken, and the ether dissolves off all 

 the oil. 



This is sufficient as regards the puncturing instrument, but it is of the 

 utmost importance that the end of the cone shall be not only free from 

 fibrin ferment, but that it shall also be free from any dust, or anything else 

 which might impede the flow of the blood. 



In the first place, to clean the drop of coagulated blood from it, it is put 

 under a strong jet of water. Then it is washed in absolute alcohol, and put 

 into the hot oil. After rinsing in ether, a perfectly clean handkerchief, 

 made of fine silk, is dipped in ether, and drawn once or twice gently 

 across the end of the cone. After this treatment, the cone is fitted into the 

 neck of a small bottle, and thus preserved from contamination with dust 

 until it is required. 



The following is the method which I find best fitted to obtain at once 

 a drop of blood of the right size. 



A slip-knot is placed round the finger, and the arm is swung round ten 

 or twelve times. In this way the finger is filled with blood, and becomes 

 bright red. When the swinging is stopped the slip-knot is tightened up, so 

 that the condition of vascular engorgement is maintained. A superficial 

 puncture is made, and a spherical drop of blood about 4 mm. in diameter at 

 once appears. The time is then noted. 



The glass cone is gradually approached to the drop. Before it has quite 

 touched it, the blood seems to leap up, and flows smoothly right up to the 

 edge. It is put at once into the apparatus. The whole procedure, from the 

 pricking of the finger to the fitting of the cone into its position, should 

 not take more than 10 seconds. 



Jenner's vaccinostyles are well adapted for pricking the finger, but it 

 is necessary to fit them with a guard of some description, to prevent too 

 deep a puncture being made. 



If the wound is too deep, the drop of blood is apt to spill over, and 

 a stream runs from the puncture, from which it is impossible to obtain 

 the proper quantity of blood. The only way to get a constant amount 

 of blood on the end of the cone is to produce a drop of the right size. 

 This is a difficulty in dealing with people who have not been pricked 

 before, for there is a considerable variation in the rate of flow in different 

 individuals. 



That the size of drop taken up by the cone should be approximately 

 constant, is of considerable importance. Variable results are obtained if 

 this point is neglected. 



As soon an the cone has been introduced into the box, the reservoir must 

 be raised to a little more than twice its original height. This is necessary 

 because a higher initial pressure is required, partly to overcome the inertia 

 of the corpuscles, but mainly, I think, to break up the blood from the 



