The prince marvels at the huge belts and wheels turning throughout this level. Elika, on the other hand, says machines are evil and should be torn down. She wasn't so hard on technology back in the Windmills when she was praising the workers and their grinding gears. Through out this encounter the way the princess would rule is being more apparent and I am seeing hints toward a pro-worker anti-technology socialist state.
The Alchemist:
In his final moments, the Alchemist hucks a huge ball of corruption at the Prince and then vanishes. Elika can't remove it herself but she thinks that if they can just get up to the fertile ground she can strip the tar from him. Contrary to fifth rule video games, in which an infected protagonist becomes stronger when infected by the enemy, the corruption doesn't give the prince any magical powers like summoning a plague of hornets or tentacles. It does make the screen borders black like you have a vision problem. Based solely on studying the posters at the ophthalmologist's office, I would say that this is a corruption induced glaucoma.
At the top of the platform ridge is the fertile ground. Just as the princess had suspected, healing the ground also removed the corruption from the prince and the camera's temporary glaucoma.