Complement??

[rex]

Hi there i'm a 2nd yr. Biomedical student who's having a problem
understanding the whole concept of complement.  I need to write an
essay about it but do not know where to begin.  Can someone please
give me a brief description of what complement is or point me to the
right direction.  I can imagine this to be a big subject but any help
will be very much appreciated.

Thanks  

any reply e-mail to:                 rrreyes at enterprise.net