But something touched him in Java, and it changed his life. Whether or not it changed history is moot. But insight came on Mayer in 1840, and science historians still talk about it. He was letting blood from sick sailors. You do that by lancing a vein.
Venous blood carries less oxygen than arterial blood.
It runs darker. The first time Mayer opened a vein in Djarkata, blood ran far too red. He thought he'd hit an artery. Then he found that's normal in the tropics. They generate less heat.