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Some time ago I had difficulty in removing small quantities of separated serum from a small, narrow centrifuge tube. The usual method of capillary attraction with a fine-bore glass tubing pipet failed, owing to the fact that if I tipped the tube sufficiently for the pipet to act, the serum movement would cause the sediment to mix, defeating the object, which was separation of the serum. In a wide tube it is not difficult to raise the capillary point of the pipet higher than the finger end, high enough to increase the flow materially.
Narrow tubes are much more of a problem. My experience with Wright's pipets for blood collection gave me an idea which I have not seen mentioned. The end of the drawn out part of the pipet, a millimeter in diameter, is carefully flamed so that it curves about 45 degrees, say about one quarter-inch from the
Huber JE. A NEW PIPET. JAMA. 1915;LXV(15):1279. doi:10.1001/jama.1915.25810150002018b