Now the question is what exactly is the composition of feces? So feces is composed of water. It contains dead bacterial cells that basically have been killed by some type of agent. For example, the high acidity of our stomach kills all bacterial cells and those cells end up in the feces that we excrete to the outside of our body to the outside environment of our body. Now, feces also contains something called roughage. Roughage, for example, consists of some type of indigestible material such as cellulose.