rubber bulb. its a bit like the end of an eye dropper if you ever used the old fashioned kind. The modern ones are actually sorta complex where you can let go and the liquid will stay inside and you press an area near the kneck which will release the vacum. back in those days it was just a bulb and a bit frustrating to use so they did this dangerous technique.
Basically it took many years before someone developed something that could be run with a trigger or button. Before that you used a vacuum (your mouth) to pull liquid into a pipette. Heard an older chemistry professor talk about a colleague who years before swallowed a salmonella sample by accident. A lot of people surely got hurt this way.