Throughout history, mothers who could not breastfeed their babies either employed a wet nurse[85] or, less frequently, prepared food for their babies, a process known as "dry nursing".[85][86] Baby food composition varied according to region and economic status.[86] In Europe and North America during the early 19th century, the prevalence of wet nursing began to decrease, while the practice of feeding babies mixtures based on animal milk rose in popularity.[87][88]