" Your spirit shouldn’t be ‘fine.’ It should be effervescent.”

The “spirit” in question wasn’t the soul. Nothing so abstract. It was spirit of the body—the clear fluid pumped by the second heart through its own network of vessels, subtler and more mysterious than the primary vascular system. Its function wasn’t properly understood by science. You could live even if your second heart stopped and the spirit hardened in your veins. But it did have some connection to vitality, or “passion,” as Master Hyrrokkin said, and those without it were emotionless, lethargic. Spiritless. "

― Laini Taylor , Strange the Dreamer (Strange the Dreamer, #1)