Introduction to Blood cells
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/B/Blood.html
Clotting
http://www-admin.med.uiuc.edu/hematology/
Immune system
ttp://www.nobel.se/medicine/educational/poster/1996/introduction.html
Mast cells
http://www.nlm.nih.gov/medlineplus/ency/imagepages/19333.htm