In the Shenandoah Valley and Peninsula Campaigns of 1862, Union and Confederate soldiers faced unfamiliar and harsh environmental conditions--strange terrain, tainted water, swarms of flies and mosquitoes, interminable rain and snow storms, and oppressive heat--which contributed to escalating disease and diminished morale. Using soldiers' letters, diaries, and memoirs, plus a wealth of additional personal accounts, medical sources, newspapers, and government documents, Kathryn Shively Meier reveals how these soldiers strove to maintain their physical and mental health by combating their deadliest enemy--nature. Meier explores how soldiers forged informal networks of health care based on prewar civilian experience and adopted a universal set of self-care habits, including boiling water, altering camp terrain, eradicating insects, supplementing their diets with fruits and vegetables, constructing protective shelters, and most controversially, straggling. In order to improve their health, soldiers periodically had to adjust their ideas of manliness, class values, and race to the circumstances at hand. While self-care often proved superior to relying upon the inchoate military medical infrastructure, commanders chastised soldiers for testing army discipline, ultimately redrawing the boundaries of informal health care.