function verificar()
	{
	error='';

		if (document.form.apellido1.value=='') 
		{
			error=error + '1st Surname.\n'; 
		}

		if (document.form.apellido2.value=='') 
		{
			error=error + '2nd Surname.\n'; 
		}

		if (document.form.nombre.value=='') 
		{
			error=error + 'Name.\n'; 
		}

		if (document.form.email.value=='') 
		{
			error=error + 'E-mail.\n'; 
		}
		
		if (document.form.consulta.value=='') 
		{
			error=error + 'Consultation you want to make.\n'; 
		}
	
	if (error=='') 
	{
		document.form.submit();		
	}
	else
	{ 
		error="The following data are necessary\n" + "or they are erroneos:\n\n" + error + "\n" + "please, verify these data." ;
		alert(error);	
	}

}