The Bacillus of Long Life
 A Manual of the Preparation and Souring of Milk for Dietary Purposes, Together with an Historical Account of the Use of Fermented Milks, from the Earliest Times to the Present Day, and Their Wonderful Effect in the Prolonging of Human Existence

by Loudon M. Douglas

"The Bacillus of Long Life" by Loudon M. Douglas is a scientific publication written in the early 20th century. The book examines the preparation and dietary significance of soured milk, detailing historical practices and scientific findings regarding its effect on human longevity. It discusses the health benefits associated with fermented milks and the role of bacteria in promoting life extension. At the start of the book, the author outlines the ancient history of milk consumption and emphasizes its longstanding importance in various cultures, particularly in Eastern Europe. The opening delves into the methods of preparing fermented milks, such as koumiss, keffir, and yogurt, and introduces evidence suggesting that regions where these sour milks are prevalent tend to have higher numbers of centenarians. Douglas presents anecdotes and historical references, setting the stage for a deeper exploration into the microbiological and nutritional aspects of these milks in subsequent chapters.