Assign MovieClip instance name to variable

Hi,

Does anyone know how I can assign a movieclip instance name to a variable, so that I can use reference it?

For example:

var mcName:String = “box2_mc”
mcName.play();

It wont work and I get the error:

1061: Call to a possibly undefined method play through a reference with static type String.

Should I define it as another datatype?

Best regards.