In 1901, Joseph Hoeing Kastle and Oliver March Shedd in the U.S. found that biological material could cause the oxidation of phenolphthalin to phenolphthalein in slightly alkaline solutions. In 1903, Erich Meyer in Germany found that blood cells could also trigger the reaction.  In 1906, Kastle and Amoss found that chick hemoglobin in blood triggered the reaction. In 1909, Kastle found that the test was sensitive to very dilute samples of blood. However, in 1908, Pozzi-Escot (who by then was living in Lima, Peru) found that the test produced false positive reactions in response to a number of substances besides blood.