Complex sentence: In the mid- 1890s with physiologist Nathan Zuntz (1847--1920) and others, he began investigations involving physiological effects on the body associated with air pressure and altitude change, and in 1896 made the first in a series of several high-altitude balloon ascents.
Split into simpler sentences: In the mid- 1890s with physiologist Nathan Zuntz (1847--1920) and others, he began investigations involving physiological effects on the body associated with air pressure and altitude change. In 1896 made the first in a series of several high-altitude balloon ascents.