Both past and present-day scientists have suspected the intestines of playing a role in various diseases. Present-day studies focus on the intestinal flora's role in physical diseases such as diabetes and overweight, while others seek to establish a connection between the intestinal flora and e.g. autism, schizophrenia and depression. But even modern-day scientists have difficulties studying the around 500-1000 different species among the approx. 100 billion active bacteria in our intestines.