The liver regulates most chemical levels in the blood and excretes a product called bile. This helps carry away waste products from the liver. All the blood leaving the stomach and intestines passes through the liver. The liver accounts for up to 100% of a person's blood filtration along with the kidneys, and 50% of a person's metabolism. Destruction of the liver is instantly fatal.
While most animals have livers, the liver item can only be acquired by harvesting them from human pawns through the surgery bill. This bill requires 1 of any type of medicine to perform. Success chance is dependent on a number of factors, including bed quality, room cleanliness, and doctor skill - specifically the doctor's Medical Surgery Success Chance.
Removing a liver from a guest or prisoner decreases faction goodwill by 20 points for organ harvesting, as well as 6 points for murder, down to a max of -100, and creates a -5 mood to your pawns for 8 days due to "someone's organ harvested", stacking up to 5 times, with a 0.75x multiplier.
Because removing the liver is invariably fatal, removing it from your own colonist can give tremendous mood penalties. -5 for "Colonist organ harvested", -6 for "Colonist organ-harvested" which is fatal organ harvesting which stacks with the first, as well as penalties for anybody who participated in or was friends with the colonist. -3 for "My friend died", -4 for "Observed corpse", -5 for "Witnessed ally's death." If you intend to harvest a liver from one of your own colonists, be very careful about managing mood afterwards, especially for the doctor who carries it out.
Pawns with the Bloodlust and Psychopath trait are not affected by the harvesting of other people.
While livers can be harvested from prisoners, guests, and your own colonists, generally it is preferable to harvest from prisoners because removing the liver is fatal. Killing a guest or your own colonist carries a significant mood penalty.
There are two primary reasons to harvest an organ - trade and transplantation.
Livers can be damaged by disease, drugs, or combat. Damage to the Liver reduces Blood Filtration (up to 100% when totally destroyed) and Metabolism (up to 50% when totally destroyed). This has several effects - the first is up to a 10% reduction in Consciousness which in turn affects almost every task a pawn can perform - making them slightly worse in basically every way.
The second, perhaps more urgent, effect is up to a 50% reduction in Immunity Gain Speed based on damage to Blood Filtration. This significantly reduces the survivability of infections and common diseases such as the Flu. If a pawn has an immunity gain speed of 58% or lower because of damage to the liver or kidneys, then the flu will be invariably fatal.
Finally, damage to the Metabolism capacity reduces the Rest Rate Multiplier which makes a pawn sleep for longer periods to become fully rested.
Total destruction of the liver is instantly fatal. Thus, it is recommended to replace damaged livers on valuable colonists as soon as possible.
Each liver is worth 500 silver, and only has a mass of 2. The abundant supply of raiders means that, if the mood penalty can be withstood, a significant amount of value can be extracted from them without having to keep prisoners and wait for a Slave Trader or Royal Tribute Collector .
Because removing the Liver is fatal, it's actually suboptimal to remove when the other organs are all okay. The Heart, Lungs, and Kidneys are also options for harvesting. If willing to organ-murder the donor, the optimum is removing:
- 1x Lung worth 400
- 1x Kidney worth 250
- 1x Heart worth 500
For a total of 1150.
If the Heart is unavailable you can take the Liver instead which has the same value but weighs twice as much. If that is also unavailable, the second lung and then the second kidney are the optimal options. Removing the heart, liver, second lung or second kidney are all fatal and prevent further harvesting.
If unwilling to organ murder the donor, the best option is to harvest
- 1x Lung worth 400
- 1x Kidney worth 250
For a total of 650.