This has come up on another board, but the term monthly nurse was also used as a euphemism for wetnurse particularly towards the end of the 19th Century when people were getting a bit sqeamish about things, and bottle feeding was making advances through the introduction of condensed milk. Wet-nurses wee employed because the baby food made was oftrn of inferior quality rgickebedwith cornflour, and in come gistricts the water supply was not very good. There is a good account of the practice in the novel 'Esther Waters' by George Moore in 1894 (free ebook from Gutenberg project)