(a) (Physiol.) The fluid which at one time was supposed to circulate through the nerves and was regarded as the agent of sensation and motion; -- called also the nervous fluid, or nervous principle.
(b) Physical health and energy; frolicsomeness; sportiveness.
She had high animal spirits, and a sort of natural self-consequence, which the attention of the officers, to whom her uncle's good dinners, and her own easy manners recommended her, had increased into assurance.
Jane Austen. Pride and Prejudice (1813)
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"But why on earth should he play a trick like that on Professor Derrick, Chase?"
"Pure animal spirits, probably. Or he may, as I say, be a minion."
P. G. Wodehouse. Love Among the Chickens A Story of the Haps and Mishaps on an English Chicken Farm (1909)