JQuery :: How To Refer Nested Field In Multidimensional Array

I'm using getJSON to retrieve information from a header record and the corresponding detail records and display the detail records in a table. The PHP script that is called returns a JSON string (via json_encode) that looks like this:

{
"srn":"1",
"invNo":"1",
"custNo":"39750",
"purchOrd":"PO12345",
"shipVia":"our truck",
"jobNo":"E001-11",
"invDate":"8/3/2011",
"taxCode":"1000000",
"shpName":"testName", .....

Here is the html table:
<table><thead><tr>
<th colspan="2" >Item Description</th>
<th>Quantity</th>
<th>U/M</th>
<th>Item Price</th>
<th>Item Amount</th>
</tr></thead><tbody>
<tr class="p_row_1"> .....

And here is the $.getJSON:
$.getJSON("GET_INV_INFO.php",{srn:'<?php echo $srn; ?>'},function(s){
// Get Header Info
$('#ip_invNo').html(s.jobNo);
$('#ip_invDate').html(s.invDate);
$('#ip_custNo').html(s.custNo);
$('#ip_purchOrd').html(s.purchOrd);
$('#ip_custName').html(s.custName); .....

My problem comes in the getJSON section where I'm trying to populate the table with a record. I don't know how to refer to the different fields in array 's'. I've tried the following and many variations, but to no avail:
$('.p_row_'+i+':nth-child(1)').html(s.row.i.itemNo);
$('.p_row_'+i+':nth-child(1)').html(s.row[i].itemNo);
How do I refer to a nested field in a multidimensional array like this?