reading json object with jquery

using json like

( {"Records": [ {"firstname":"Nancy","lastname":"Davolio"} ],
"RecordCount":"1" } )

and jquery like:

 $.ajax({
....

    success: function(json, status) {
     if(json.Records){alert("firstname= "+json.Records.firstname );}
....

I can retrieve values for firstname if I use the reference spelled out

is there a way to get it by numerical position, something like:

  if(json.Records){alert("firstname= "+json.Records.0 );}

except it would work .. :)

thanks in advance