The origin of the idiom to vent your spleen dates back to Hippocrates in 400 BC.
The belief endured until the nineteenth century that four bodily fluids controlled physical and mental qualities.
Blood, phlegm, yellow bile, and black bile were called humours. The word humour, or humor in US spelling, derives from Latin, meaning liquid or fluid.
It was yellow bile, which was thought to be responsible for anger and restlessness that the idiom vent one’s spleen derives.
The four humours and the spleen
In medieval science and medicine, balancing the four bodily fluids was believed to lead to good physical and mental health.
For example, too much yellow bile could induce a fever by making the body hot and dry.
The treatment was to eat more cold foods like lettuce or cucumber, which were wet and cool.
By doing so, it helped to redress the imbalance in the humours.
But it was the importance of emotions and characteristics that led to the anger idiom.
The table below shows how the four humours were believed to affect temperament and personal characteristics.
But for the origins of the idiom, it was the yellow bile that was defined as choleric, meaning bad-tempered or irritable.
If the body produced too much yellow bile, it could lead to a person becoming angry very easily.
Now we are getting close to the origin of vent your spleen.
The wrong organ
However, the spleen, a small organ in the upper left abdomen, behind the stomach, doesn’t produce bile.
It is a product of the liver.
But until the advent of modern medicine, this wasn’t the understanding, so the spleen got the blame.
If you want to dig deeper, you can read this in-depth article about the history of the four humours.
What does vent mean?
When we use the verb vent with an object, it means giving free expression, especially to a strong emotion.
It can also mean providing an outlet.
But this sense is generally to do with an outlet for air, gas, or a liquid.
So for the anger idiom, vent means an action to release one’s anger or irritability.
When you vent your spleen, you express your anger.
It is often passionate, emotional, and over the top.
You could also say that it is to air your grievances.
There are a handful of other idioms that use the verb.
Examples include, need to vent (to someone), give vent to something, and give (full) vent to (something).
The spleen in literature
William Shakespeare used the word spleen, but more in the sense of melancholic than choleric.
In Julius Caesar, he uses it to describe the irritable nature of Cassius.
Under your testy humour? By the gods
You shall digest the venom of your spleen,
Though it do split you; for, from this day forth,
I’ll use you for my mirth, yea, for my laughter.
Le Spleen de Paris, also known as Paris Spleen, is a collection of poems by Charles Baudelaire.
The collection was published posthumously in 1869.
Again, the sense of the spleen is melancholic rather than of anger.
The poem, The Spleen by Anne Finch was published in 1701.
What art thou, SPLEEN, which ev’ry thing dost ape?
At the time, the spleen was often a metaphor for depression.
The belief was that a splenetic or depressed person had an excess of yellow bile.
Body parts idioms in writing
Writers use idioms all the time in writing. Body parts idioms are one of the most common examples.
Very often, we use them without thinking. But I always think it is interesting to investigate the origins of certain idioms.
While vent your spleen is a good example because it is a little obtuse, many others have intriguing origins.
Many might think that stabbed in the back relates to the assassination of Julius Caesar. However, its origin is much later.
According to The New York Times in 1989, the infinitive phrase to stab in the back was first used figuratively by George Bernard Shaw in a New York Times Magazine article in 1916.
However, most of the external body parts idioms are generally literal in meaning.
I’ll give you a hand. (to help)
I need a shoulder to cry on. (Emotional support)
You might have to twist his arm. (Persuasion)
Oh, keep your chin up. (Stay happy)
It goes in one ear and out the other. (Doesn’t listen)
My lips are sealed. (I won’t say a word)
There are hundreds more that are in everyday use.
Internal body parts
However, there are far fewer idioms that relate to internal organs.
When we use them, the meaning is often more figurative or metaphorical.
It broke her heart. (overwhelmed by sadness)
He didn’t have the stomach for it. (not brave or determined)
I had a feeling in my bones that it would happen. (have an intuition)
Jim was sweating blood, waiting for his exam results. (very anxious and tense)
Mary really gets on my nerves. (To irritate)
The most commonly used organ in idioms is the heart. There are so many that relate to romance, generosity, and bravery.
But it’s difficult to find any about the lungs, kidneys, pancreas, or intestines.
Good writers are always inquisitive.
I must admit that I often wander off researching an event, person, word, phrase, or in this case, an idiom.
So much so that I forget to get on with what I was writing.
But that’s what we do when we write. If something pops up that we are not sure about or seems intriguing, we have to investigate.
In my case, it was the discovery that the word humor (or humour) could mean liquid or fluid, as well as being amusing or comic.
So that’s how I stumbled on the link between the spleen and the expressions relating to anger.
I found it all so interesting that I couldn’t help myself. I had to write about it.
Now all I need to do is remember what I was writing about at the time of my little discovery.
Related reading: Bated Breath And Baited Breath Always Cause Confusion