Example 3: Take four capsules of Dr. Schulze 's "Intestinal Forumla #1"(TM), wait 12 hours & report back.
Example 4: Phenolphthalein. Eat a gram, and report back. Don't leave home.
Example 5: Beck's(TM) Beer. Drink six of those and see what you get in the morning.
Diaharhea, or however it's spelled, can have many causes and doesn;t always require a "pathogen" to be present.
The host is akin to a field. Fertile ground can grow many things and additionally one may treat the land with various materials. The possibilities are nearly unlimited. Fortunately, the human system was designed so that most of what may be planted from time to time is not detrimental to the organism as a whole, although once in a while some may seem to have a similar effect as though a grassfire has occurred. Even the aftermath of a grassfire is be a blessing provided that one knows how to take advantage of the situation.