A human torso model is designed to be as accurate as possible so that students/researchers can understand the inner workings of the body. Therefore, the organs have been designed to be the same size of an actual human being of that stature, while also being in the correct position within the body to better understand the interrelationships between the organs. The only thing that is not accurate in these models is the texture of the organs as most are smooth plastic unlike the actual organs.
The substance must be able to alter its physical characteristic (for example, its color) in accordance to a change in pH. One example of this is litmus paper, which becomes red under acidic conditions and blue under basic conditions.
