Hugh Lofting 
Story of Doctor Dolittle [PDF ebook] 
Being the History of His Peculiar Life at Home and Astonishing Adventures in Foreign Parts Never Before Printed

Respected physician John Dolittle swaps human patients for animal ones as his parrot Polynesia teaches him the secret of talking to the animals. His fame spreads and he travels to Africa to treat a monkey epidemic. Setting out with his favorite crew of creatures, Dolittle must face trial after trial; being shipwrecked, escaping the king of Jolligingki and figuring out what do do with a pushmi-pullyu, the shy two-headed gazelle-unicorn cross.