Blood cell
A blood cell was a ular component of an animal's blood, pus (in the case of white blood cells, which also made up the immune system), and plasma (in the case of platelets).

Normal blood cells (i.e. the ones that made blood, also known as erythrocytes), were red in Humans, Talaxians, () and Kazon, () green in Vulcans, and brown in Cardassians. ()

Too many blood cells could result in polycythemia, which could make the subject ill, though not always. ()

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Biology
Anatomy