Glass surfaces are negatively charged, and when blood is collected in a clean glass test tube, it clots. Explain this observation.
it doesnt matter if it's glass or plastic. Once exposed to air (oxygen) the blood will clot unless it's been treated with an anticoagulant like EDTA, heparin, or sodium citrate. That's why these test tubes have anti coagulant in them. The tubes themselves can be glass or plastic, it doesn't matter. No anti-coagulant = clot anti-coagulant = no clot.
