ckeditor 4: don't work with form created by ajax

I'm back :)

So, I use a form generate by ajax request like this:

PHP file:

if($type=='BLOB' and $type_form=='text')
            {         
                echo '<textarea class="ckeditor" id="'.$nom.'" name="'.$nom.'">';
                    echo $donnees[$i];
                echo '</textarea>';  
            }

JS file:

function form(table,id)
{
  div_sup();
    instance_ajax('http'),
     http.open("GET", '../php/form.php?table='+table+'&id='+id, false);    
     http.send(null);
    document.getElementById('fondnoir').style.display='block';
    document.getElementById('fond_contenu2').innerHTML=http.responseText;          
} 

 And generated file:

<form action="../php/traitement.php?table=content&amp;id=4" method="POST" name="affiche_grille">

<input type="hidden" id="ID_CONTENT" name="ID_CONTENT" value="4">

<label>Page:</label> 
<input type="text" id="PAG_CON" name="PAG_CON" value="protu"><br>

<label>Image:</label>
<input type="text" id="IMG_CON" name="IMG_CON" value="bxcb"><br>

<label>Titre FR:</label>
<input type="text" id="TFR_CON" name="TFR_CON" value="xcbxcb"><br>

<label>Description FR:</label>
<textarea class="ckeditor" id="DFR_CON" name="DFR_CON">xcbxc</textarea><br>

<label>Contenu FR:</label>
<textarea class="ckeditor" id="CFR_CON" name="CFR_CON">bxcbxcbx</textarea><br>

<label>Keywords FR:</label>
<textarea class="ckeditor" id="MFK_CON" name="MFK_CON">cbxc</textarea><br>

etc..

<input type="submit" id="c_submit" name="c_submit" value="Valider"></form>

Normally, all textarea should be replaced by ckeditor ? I use class="ckeditor"... And with a single html or php, it work good but with this ajax code, nothing is replaced.

What's the problem ?