Mailer class error

I created a helper method in a file called mailer_helper.rb that I
want to use in my mailer class. I included the helper using this
statement:
helper :mailer
even after including this I get this error:
undefined local variable or method `get_host’ for #Mailer:0x38aca0c
any ideas?

class Mailer < ActionMailer::Base

helper :mailer

def contact_us(contact_us)
@subject = ‘Nu+riSum contact request’
@recipients = ‘[email protected]
@from = contact_us.email
@sent_on = Time.now
@layout = :mailer
@body =
{
:fn => contact_us.first_name,
:ln => contact_us.last_name,
:em => contact_us.email,
:org => contact_us.organization,
:ph => contact_us.phone,
:msg => contact_us.comments,
:host => get_host
}
end