This episode, we take a sip of tonic's history with Kim Walker and Mark Nesbitt, authors of the new book Just the Tonic: A Natural History of Tonic Water. Kim Walker and Mark Nesbitt are the authors of the new book, Just the Tonic, A Natural History of Tonic Water, published by the Royal Botanic Gardens, Kew. Kim made her own tonic from cinchona bark, and cinchona bark is certainly available for purchase.