Solved cryptogram
The inner surface of your lungs, unfolded, would carpet a fair sized room several times over.
Biology Facts, sourced to NHLBI.
What it means
Air does not exchange with blood in the big tubes. It happens in hundreds of millions of tiny sacs called alveoli, each wrapped in capillaries, and their combined area runs to something in the region of seventy square meters. Packing that much surface into a chest cavity is the whole design problem a lung solves, and it is the same trick a tree uses with its leaves.
The claim comes from NHLBI, and the page it comes from was read on 2026-08-27 to confirm it still says this.
This is not the kind of claim that goes out of date, which is why it was set as a puzzle rather than a fact with a shelf life.
Solve it yourself
This fact is a cryptogram here: 75 letters over 21 different ones, graded hard.
- SourceNHLBI
- CollectionBiology Facts
- Difficultyhard
- Length75 letters, 21 of them different
Nearby in the collection
The facts either side of this one.
- NIDDKhard, 74 letters
- NHLBImedium, 74 letters
- MedlinePluseasy, 72 letters
- MedlinePlushard, 76 letters
About as hard as this one
Scored closest to it by the model behind our guide to solving cryptograms.
- U.S. Geological Surveyhard, 66 letters
- NIDCDhard, 74 letters
- National Human Genome Research Institutehard, 67 letters
- Royal Society of Chemistryhard, 70 letters