Probiotic capsules. These contain bacteria that are intended to supplement the natural, beneficial bacteria essential to the healthy functioning of the human digestive system. Most of these bacteria are found in the intestines, as very few bacteria can survive the acid conditions of the stomach. It is known that certain bacteria survive the stomach acid, but it is uncertain whether they then always successfully colonize the patient's intestines, or whether continuous probiotic therapy is needed. It is thought that the most important benefit is the defence probiotic bacteria provide against harmful pathogenic micro-organisms.