Cellular metabolic activity, i.e., the many vital biochemical processes executed by different cell types in the various tissues and organs, result in a variety of unnecessary metabolites or end products, which must be removed from the system. Excessive amounts of nutrients, such as water, electrolytes, and minerals, must also be eliminated in order to maintain the physiological equilibrium of many body systems, such as neural activity, cardiac function, and blood pressure. Through respiration, the lungs deliver oxygen into the blood circulation and collect carbon dioxide from the venous vessels, to be eliminated through exhalation. The process of digestion requires the elimination of non-absorbable substances and other compounds that are excreted from the body in the feces. One-fourth of the fecal matter that is eliminated from the intestines is constituted by solid matter and the remainder is water. The fecal solid matter usually contains...