Most people don't know about the things that go on above and below the exhibits of El Museo. Out of sight of schoolchildren and families is a whole different side to the museum's life, a life that's responsible for the public areas even being there (though the directors would like to think otherwise). A life, ironically, of death.
In the partially darkened upper and lower crypts the corpses are kept in long cabinets and shelving. Millions are impaled on iron pins, skinned and mummified, or drowned and pickled in Very Near Everclear (food grade, even). The air smells strongly of moth ball pesticides, and faintly of other solvents. This is a tomb, a catacomb, a morgue. And yet, the atmosphere is nothing if not cheery. The curators sit as grim reapers, collaborating with the collection managers to the sisyphian task of bringing order out of unending chaos. There are always new bodies coming in, we would have it no other way. More bodies means more study, but also more work. This is no funeral; the biologist undertakers are lovers of life and that's /why/ they are in this line of work. A thousand questions could be answered by just one of the specimens, studied under the right light, carefully enough. Each one is like a record in a government archive, well, that is if every record was an encyclopedia onto itself.
The reaping is a somewhat sad operation, but the Guardians of Natural History live with their guilt by trying to make amends. It may be thirty, 100, hundreds of years before someone retrieves a particular drawer for study, but they're meant to last. The preserved individuals, protected from mold, insects and climate, would last unto fossilization under these conditions. All this information, once lost, would never be regained. And it sustains the life of El Museo, like a great benevolent beast who eats the dead to bring forth new growth.