"When the body is disordered,or exhausted with fatigue, the soul frequently hides herself in sleep, and retires from external things, in order that she may be more at leisure to recruit the body, or to rectify what has happened amiss in it; and hence the inclination to sleep after child-bearing: hence, also, the frequent sleeping of infants; whose anima, it seems, is so taken up with directing and governing the vital motions, that it has little time to attend to any thing else."
An Essay on the Vital and Other Involuntary Motions of Animals
3 entries in ESTC (1751, 1763, 1768).<br>
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Robert Whytt, <u>An Essay on the Vital and Other Involuntary Motions of Animals</u> (Edinburgh: Printed by Hamilton, Balfour, and Neill, 1751). &lt;<a href="http://books.google.com/books?id=eCz7KJ_6XYIC">Link to Google Books</a>&gt;