Your body defends itself in three layers. First is a wall that keeps invaders out. Next come fast, all-purpose troops. Last is a slow but exact special force. Tap each line.
First line
Lines of defensethree layers deep
The three lines
📷 Reference image
A real labeled figure to compare with the interactive above.
The Lines of Defense — OpenStax, CC BY 3.0 (via Wikimedia Commons)
