Joseph Janvier Woodward, M.D., Surgeon and Brevet Lieutenant Colonel, U.S. Army, was the first pathologist at the Army Medical Museum, precursor of today's Armed Forces Institute of Pathology. In 1870 he reported a histologic study of pleuropneumonia of cattle, then a serious epizootic disease in the United States, which is: (1) The first histologic study of this disease, (2) the first scientific contribution to veterinary pathology in the United States, and (3) the first contribution to veterinary pathology from the Museum. This long-forgotten paper is reprinted here to celebrate the centenary of the latter event and to pay homage to the memory of its author.