H1N1 is a subtype specie of Influenza A virus. H1N1 Influenza Virus has mutated into various strains such as the Spanish Flu strain， mild human flu strains， endemic pig strains， and various strains found in birds.
The Influenza A Virus is a globular particle about 100nm in diameter， sheathed in a lipid bilayer derived from the plasma membrane of its host. Studded in the lipid bilayer are two integral membrane proteins some 500 molecules of hemagglutinin （"H"） and some 100 molecules of neuraminidase （"N"）. Within the lipid bilayer are 3000 molecules of matrix protein and 8 pieces of RNA. Each of the 8 RNA molecules is associated with many copies of a nucleoprotein， several molecules of the three subunits of its RNA polymerase some "non-structural" protein molecules of uncertain function.
