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To the Editor:
—In the article (The Journal, Nov. 4, 1911, p. 1532) entitled "A Source of Error in the Test for Occult Blood in the Feces," by Dr. William A. Newbold, it is stated that watermelon pulp and juice will give a blue color with the guaiac-turpentine blood-test.It is true that the old Van Deen test, which consisted in mixing the tincture of guaiac with the oil of turpentine or peroxid and adding the urine, feces or stomach contents, will give a blue color reaction with watermelon pulp, or juice, which is identical with the blood reaction. As Weber pointed out in 1893, however, many other substances will give the same reaction, e. g., many vegetables, milk, bile, saliva and pus, as well as several medicines. He, therefore, modified the test by making an ether-acetic acid extract of the feces, to which was added the turpentine and guaiacum.
Soper HW. The Guaiac-Turpentine Test for Occult Blood in the Feces. JAMA. 1912;LVIII(26):2044. doi:10.1001/jama.1912.04260060397021
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