Hemastix are 3" plastic strips with a special blood reagent material at the tip. The strips detect the peroxide-like activity of hemoglobin in a substance. Simply rub the Hemastix on a moistened stain or across a swab that has a suspected dried blood sample on it. The reagent-coated tip will turn a shade of green if hemoglobin is detected. Compare the color reaction to the chart on the side of the bottle to determine the level of hemoglobin in the sample. If the reaction is positive, take a photograph of the strip by the substance to document the reaction and retain the strip as evidence. Please note that Hemastix® will not detect the difference between human and animal blood. Hemastix® has a shelf-life of roughly a year from the date of manufacture.