The accuracy of most methods for determining the coagulation-time of the blood depends on three main factors.
The sharpness with which the end-point appears.
Constancy between the volume of blood used for the test and its area of exposure to foreign surface.
Constancy of temperature.
These three factors have been considered in the following modification of Milian's ingenious method1 and, it is believed, make it as accurate as any method at present in use.
The instrument consists of a slide on which are mounted with balsam two glass disks 5 mm. in diameter.
Anoint the surface from which the blood is to be obtained with a thin layer of petrolatum. (This prevents contact of the blood with the skin and avoids thereby a slight source of error.) Prick the skin through through the petrolatum, obtaining, if possible, a free flow of blood. Wipe away
DUKE WW. A SIMPLE INSTRUMENT FOR DETERMINING THE COAGULATION-TIME OF THE BLOOD. Arch Intern Med (Chic). 1912;IX(2):258-261. doi:10.1001/archinte.1912.00060140132010