Have you noticed fewer holes in your Swiss cheese over the years?  Apparently this cheese (also known as Emmental cheese overseas - something I accidentally discovered for myself on residency in Iceland) had a lot of holes because small particles of hay dust used to regularly drift their way into the milk in the normal course of farming.  Our increasingly industrialized processes sterilized the cheesemaking environment so much that the holes have been mysteriously disappearing.  Now that the cause has been discovered, though, cheesemakers can judiciously add hay dust back into the milk.