When the bowel is healthy there is very little bacterial action in the small intestine. The large intestine, however, lilterally swarms with billions of these microscopic organisms. Bacterial action in the large intestine plays a major role in nutrition and digestion. These friendly bacteria synthesize valuable nutrients by digesting portions of the fecal mass. Among others, vitamin K and portions of the B complex are produced. This aspect of digestion is not completely understood and is undergoing further study. Any remaining proteins are broken down by the bacteria into simpler substances. By products of bacterial activity are numerous, such as indole, skatole, hydrogen sulfide, fatty acids, methane gas and carbon dioxide. Some of these substances are very toxic and odorous, hence the accompanying smell of feces. The brown color of feces is a result of bile pigments coming from the liver. When feces are not brown, but have a chalky appearance, there is a problem in bile secretion and digestive ability.