This paper examines the medical histories of a sample of 25,000 Union Army soldiers and veterans to study the determinants of diagnosis, discharge, and mortality from tuberculosis. We find that water and airborne diseases during the war contributed significantly to the presence of tuberculosis. Height and a higher body mass index (BMI) are also associated with protection against TB but these effects are not always robust. As an upper bound, we estimate that the contribution of modern gains in height and in BMI to the mortality decline of tuberculosis ranges from one-fourth to one-half with the rest explained by the decline in the prevalence of water and airborne diseases, especially diarrhea, dysentery, and typhoid played. The paper finds weaker support for alternative hypotheses that rely on occupational influences and exogenous changes in the virulence of tuberculosis.
