What museums are for
We are all used to visiting natural history museums to see all the animals, plants and fossils, but few people realise just how important museums are for scientists.
A museum is a bit like an iceberg, since most of it is hidden away from view (often in the cold and dark). The public face of a museum often holds less than 10 per cent of the collections, with the rest held in storage for safekeeping and use by researchers. It is often this hidden part of the collections where the real work of a museum goes on; with important scientific questions being answered by extracting DNA from specimens, sampling for radiocarbon dating, identifying new species and so on. But how are these millions of study specimens able to be stored for hundreds of years and then be found again when needed?
All organisms share some similarities and show some differences from that of their ancestors. These characteristics correspond to the evolutionary pathways taken by different organisms, so they provide information about the relationships between them. Natural history museums use these relationships as a way to organise their collections. By having organisms that are closely related stored together, in something called taxonomic groups, it becomes easy for scientists to find what they are looking for. So dogs go with cats as carnivores as part of the mammal collection in the animal section. By giving each specimen its own unique number (usually based on the year it was acquired by the museum and the order in which it entered the catalogues) it is possible to distinguish one individual organism, from the hundreds or even thousands of others that it may share a cabinet with. Most museums now use computer databases to make it simple to track down a specimen's location - much like the system used in Argos!
Ideally all related specimens should be kept together: however, the natural world is not a uniform place, and the different tissues making up an animal or plant cannot always be preserved in the same way - it's hard to keep a whole fossil tree with a single preserved leaf. In most collections there are specimens kept in alcohol (normally at about 70-80% strength), mounts (stuffed animals with glass eyes in lifelike poses), dried skins and dried plants, skeletons, frozen tissues, fossils in rocks, fossils mounted in plaster or sometimes even wax. Each type of preservation method requires different conditions for keeping the specimen in good shape, so different zones will often be used for storing a particular preservation type and the taxonomic groups will provide a sub-arrangement within these zones.
Cabinets shield the specimens from changes in temperature and humidity and prevent damage from light and physical knocks. Jars must be kept topped up with alcohol to prevent drying out, and every so often specimens may need to be cleaned with brushes or special vacuum cleaners. The materials used in museum collections have to last indefinitely, so they are free of acids and chemicals that break down over time.
Generally, all of the organisms in a museum store are dead (except the staff, and sometimes even they seem pretty close). Live animals, plants and fungi are a major problem since they can damage, or attract pests that will damage, the specimens. Most museums will monitor the insect population using sticky traps, checking to make sure that there are no pests. If pests are found it can be very hard to get rid of them, particularly without using chemicals that might also cause damage to the specimens (or the people using them). Generally infested specimens are frozen nowadays, but often old specimens have been treated with poisonous chemicals like arsenic and mercury, so the next time you are in a museum make sure you pay attention to signs saying "do not touch" - it may be for your own good!