The harm that some bacteria can bring about when they find their way into the organism by way of the digestive tract is so indisputable and emphatic that there has resulted a tendency to view all micro-organisms in the gastro-intestinal canal with some suspicion. Our readers are familiar with the widespread attempts in recent years to implant one type of micro-organism in the alimentary tract in the hope that it may lead to the repression or exclusion of a less desirable type. If the strictly scientific evidence for the success of such an undertaking as the implantation of the Bacillus bulgaricus or the Bacillus acidophilus on the intestinal mucosa has not been convincing, certainly the semipopular literature and the advertising propaganda have almost sufficed by mass action to enforce a respectful attitude or even a favorable impression toward the situation.
The feces literally swarm with bacteria. Osborne and Mendel1
INTESTINAL BACTERIA IN CHILDHOOD. JAMA. 1918;70(1):30–31. doi:10.1001/jama.1918.02600010028014