What is black bile?

About 2000 years ago, the Greeks believed that depression was caused by too much "black bile" in the body, and the word "depression" itself meant "black bile". They think that some people are born with black bile-depressed individuals, while yellow bile is dominant in people with bile, mucus is dominant in people with mucus, and black bile is dominant in people with depression. However, they also believe that stress, diet and seasonal changes will affect the content of black bile in the body. Nowadays, we abandon the old theory of "black bile" and look for the cause of depression by studying the changes of brain chemistry. Unfortunately, however, we are not as speculative as the Greeks: some people think that brain chemical changes lead to depression, but although those depressed patients do have brain chemical changes, it does not mean that brain chemical changes lead to depression. For example, we know that there is a certain relationship between adrenaline secretion and anxiety, but this does not mean that adrenaline is the direct cause of depression, nor does it mean that lowering adrenaline can treat anxiety. For example, if a robber forces us to give money, our adrenaline level may rise, which will make us have a certain anxiety experience. If you want to get rid of this anxiety, the effective way is to get rid of robbers instead of taking some drugs.