An essay is presented the encyclopedic book "The Book of Worlds" or "Sefer ha-'olamot" or "Ma'ase Tuviya," by early modern Jewish physician Tuviya Cohen, also known as Tobias Cohn or Tobias Katz. It considers his medical education and his tutor Salomon Conegliano, also known as Conian. Cohen's views on physiology, the humors, and the organs, including the heart and arteries, are considered.