grid deduction - Double feature: In cold blood

_{This puzzle is part 5 of the Double feature series (first part here). The series will continue in "Double feature: Legal trouble".}

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Rules of Nurikabe¹

• Shade some cells in the grid.


• Numbered cells are unshaded.


• Unshaded cells are divided into continuous regions, all of which contain exactly one number. The number indicates how many cells there are in that unshaded region.


• Regions of unshaded cells cannot be adjacent to one another, but they may touch at a corner.


• Shaded cells must all be orthogonally connected.


• There are no groups of shaded cells that form a $2\times2$ square anywhere in the grid.

Across
2. Fine threads of Nazis holding top-tier currency (7)
5. Turn over some journalism lab meat preserves (7)
7. Ancient Greek city moving to China (7)
9. Engulfed in boiling liquid (3)
11. Drive in a nail at the end of hotel's staircase support (8)
13. Taking in incomplete additional dose of sugar (8)

Down
1. Source of blue dye from Manila (4)
2. Tuscan city welcoming new brownish colour (6)

3. Law exam returned by business intelligence teacher (5)
4. To start off, Sukarno is Indonesia's first president (4)
6. Foolish spectator's heart becoming extremely lonely (7)
8. Document written up from Latin manuscript (5)
10. Three lost in the middle of sandbar region in Germany (4)
12. Treatments for infectious disease (4)

_{¹ Paraphrased from the original rules on Nikoli.}

Solve both puzzles to answer the question: What is found in blood?

Answer

Solution, with cryptic clue explanations:

So the answer is ANIMAL MITOCHONDRIA.