how to pas json data to webmethod using jquery ajax

how to pas json data to webmethod using jquery ajax

in asp.net i have on web method which tales list of patient as an argument how to pass this list using jquery
my code is

function

 testsave() {

$.ajax({

type:

"POST" ,

url:

"Default.aspx/tests" ,

contentType:

"application/json; charset=utf-8" ,

dataType:

"json" ,

data: dtata.d,

//"{'pes':'" + dtata + "'}",

async:

false ,

success:

function (response) {

},

error:

function () {

alert(

 "Error" );

}

});
but getting error