Casting objects - Polymorphism

Hello,
let's take this code:

SuperStrict

Type TAlien
	Field health:Int = 1
	'
	Method PrintHealth()
	
	End Method
End Type

Type TAlienSmall Extends TALien
	Field health:Int = 2
	'
	Method PrintHealth()
		Print "Method PH in TAlienSmall"
	End Method

End Type

Type TAlienBig Extends TAlien
	Field health:Int = 3
	Method PrintHealth()
		Print "Method PH in TAlienBig"
	End Method
End Type

' Main
Local alienlist:TList = New TList
Local as:TalienSmall = New TAlienSmall
Local ab:TAlienBig = New TAlienBig

alienlist.AddLast(as)
alienlist.AddLast(ab)

For Local alien:TAlien = EachIn alienlist
	Local castedalien:TAlien = TAlien(alien) ' casting type of object
	'
	castedalien.PrintHealth
	Print castedalien.health
Next

With the line "Local castedalien:TAlien = TAlien(alien) "
I can call the right methods of the objects, but how
do I get access to the fields of the objects that are not Baseobjects?
I can use a method like "ReceiveHealth:Int()" which will
return the correct value(2,3) but is there a smarter way?