The terrain theory is the theory of disease proposed by Antoine Béchamp that a diseased body, the "terrain", will attract germs to come as scavengers of the weakened or poorly defended tissue. Béchamp believed that the pH of the body is important, and that an acidic pH will attract germs and an alkaline pH will repel them.
In modern science, germ theory as developed by Louis Pasteur has been the scientific consensus for many years. Germ theory states that microorganisms, bacteria, virus and fungi, are the cause of most diseases. It is the cornerstone of modern medicine and treatment of disease.