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Having repeatedly observed the difficulty many students and physicians experience in acquiring an accurate technic with the coarse capillary pipettes such as are in constant use for leucocyte counting and hemoglobin estimation, it occurred to me that Wright's "throttled capillary" might be adapted to the control of these instruments.
After some experiments, the device illustrated in the accompanying drawing was found to give very satisfactory results.
—It consists of a capillary tube "throttled" in the manner described by Wright, that is, heated in a very small flame and then quickly drawn out into a fine thread. The caliber of this tip must be so fine that when gentle suction is made the air comes through very, slowly.The outer protecting tube is from 5 to 7 mm. in diameter and drawn out to an hour-glass shape. The large part of the capillary (a) is marked with a file so
BOGGS TR. WRIGHT'S "THROTTLED CAPILLARY" ADAPTED TO THE CONTROL OF BLOOD-COUNTING PIPETTES.. JAMA. 1907;XLVIII(1):47. doi:10.1001/jama.1907.25220270047002a