The Book of Vegetables (1907), by Allen French.
“Liquid manure” as spoken of in this book, can be conveniently made by immersing a bag of fresh horse manure in a tub of water. The product is strong in nitrogen, and is excellent as an application to plants which are expected to make a good stalk and leaf growth. The liquid manure should be applied dilute, and in small quantities; it should be put upon the ground, and never upon the plant itself.
It’s much easier today, to apply liquid manure to flowers and vegetables. Here’s a source for Cow Manure Tea from Authentic Haven Brand, for the modern urban farmer.