People regularly lose their spleens, for example after traffic accidents where a strong blow to the torso can rupture the small organ critically, so that it has to be removed. Surprisingly this is not as deadly as you might think. Other organs like the liver, regular lymph nodes, and your bone marrow can take over most of its jobs. And about 30% of people happen to have a second spleen that is tiny but will grow and take over the job if the first one is removed.
