Colombo put an emphasis on vivisection, the practice of experimentation or scientific research on live animals, in order to learn about the different bodily functions of the human body.
With the centrality of vivisection, the three 'rivers' was also emphasized in Colombo's book, specifically Book XI. "There are three fountain-heads, the liver, heart, and brain, from which are distributed throughout the body the three rivers of the natural blood, the vital blood and the animal spirits respectively.