6 Totally Wrong Historical Theories About What the Brain Is Made Of

We may be biased, but we think the human brain is pretty special. All this week, mentalfloss.com is celebrating this miracle organ with a heap of brain[y] stories, lists, and videos. It all leads up to Brain Surgery Live With mental_floss, a two-hour television event will feature—yes—live brain surgery. Hosted by Bryant Gumbel, the special airs Sunday, October 25 at 9 p.m. EST on the National Geographic Channel.

History has answered this with some real head-scratchers.

1. MUCUS (ANCIENT EGYPTIANS)

The Egyptian word for brain roughly translates to “skull offal,” which explains how highly they thought of it. They considered it mere organic stuffing that carried mucus to the nose.

2. SPERM (ALCMAEON OF CROTON)

Like other pre-Socratic philosophers, Alcmaeon believed semen was made in the brain and traveled down the spinal cord. Like other pre-Socratic philosophers, he was wrong.

3. PHLEGM (ARISTOTLE)

To Aristotle, the brain was basically a refrigerator that cooled the heart with phlegm. The idea is fossilized in the English language: Pituitary derives from the Latin pituita, for phlegm.

4. MARROW (TRADITIONAL CHINESE MEDICINE)

Believing the brain was an outgrowth of the all-powerful kidney, the ancient Chinese thought the head was filled with a nourishing marrow, thanks to an energy called “kidney essence.”

5. HEART STUFF (RABBI GERSHON BEN SHLOMO)

“The brain and heart share functions so when one is missing, the other alone continues its activities by virtue of their partnership,” he wrote in the 13th century.

6. ANIMAL SPIRITS (RENE DESCARTES)

In 1664, Descartes wrote that the pineal gland was the seat of the soul, flowing with animal spirits that were like “a very lively and pure flame.” The idea had been popular for centuries.