I've seen them in a KhanAcademy video, at this part: http://www.flickr.com/photos/76342179@N0…
I really don't know what it is.
I really don't know what it is.
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A mast cell (also known as mastocyte and labrocyte) is a resident cell of several types of tissues and contains many granules rich in histamine and heparin. Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being intimately involved in wound healing and defense against pathogens