If you're knitting a flat piece, change hands and use like straight needles. You push the stitches to both ends to knit the next row if you are knitting something round. If you're knitting in the round, 38 stitches may not stretch around the needles all the way, so what you can do is pinch the cord about halfway, pull it throught the stitches there and push the stitches to the ends, knit until you get to the cord. Then pull the cord out again and repeat. You may have to do this for a few rows until your piece gets long enough to fit on the cord.