What was the second section used for in Louis Sullivan skyscraper?

In Louis Sullivan's skyscraper design, the second section typically served as the "middle" or "shaft" portion, which housed offices and working spaces. This area was often characterized by large Windows to allow natural light and enhance the workspace's functionality. By focusing on verticality and ornamentation in this section, Sullivan emphasized the building's height while maintaining aesthetic appeal. Overall, it played a crucial role in the building's overall design and purpose.