Erasmus Darwin,
Zoonomia, or, the Laws of Organic Life…
(1796)
“ The teats of female animals, when they give suck, become rigid and erected, in the same manner as in the last article, from the pleasurable sensation of the love of the mother to her offspring. Whence the teat may properly be called an organ of sense. The nipples of men do the same when rubbed with the hand. ”
