This is the original cartridge filling pen, patented in 1890 (link below). A hand blown glass vial was supplied pre-filled with ink and closed with a cork. To use it, the cork was removed and the vial was mated to a soft white rubber nipple. These pens date from the 1890s and are not hard to find today. The rubber nipple will now be hard, and is typically black from ink. A quick run through your ultrasonic cleaner will show that it was once white. Back in the day, one could buy prefilled vials of ink. Since the pen was also intended to be used with standard untipped nibs, it was also sold in a box with 3 ink vials and a dozen nibs.