While at this station he was detailed, in 1877, to duty incident to labor disturbances in Pennsylvania, and sustained an injury which incapacitated him to a remarkable extent for two years.

Short terms of duty at Charleston, South Carolina, and Fort McPherson, Georgia, interspersed with sick leaves brought him to the summer of 1882, when in June he was ordered to duty with the attending surgeon in Washington, D. C. In November 1884 he himself became the attending surgeon, which post he held until November 1889.

From Washington he was ordered to Fort Logan, Colorado, where he served from May 1890 to February 1893 when he was again detailed as attending surgeon at the capital.

In April 1897 he was assigned to duty at Fort Wayne, Michigan, and from this post he accompanied the troops into the field at the onset of the Spanish–American War.

Arriving at Mobile, Alabama, he was assigned as chief surgeon of the First Independent Division commanded by Major General John J. Coppinger.

The medical department ship Bay State was placed at his disposal and he was sent to Jamaica for the purpose of acquiring information relative to the experience of the British Army in tropical hygiene.

He made a study of the housing, food, clothing, and care of troops and submitted a report with recommendations on these subjects which were of material value.

Returning from Cuba in November 1899 he commanded Josiah Simpson Hospital at Fortress Monroe, Virginia, and later was transferred to the headquarters of the Department of California at San Francisco as chief surgeon.

Unsatisfactory conditions in the army disclosed by the Spanish–American War caused the appointment by President William McKinley of the Dodge Commission.

These recommendations were briefly as follows: (1) a larger force of commissioned medical officers, (2) authority to establish in time of peace a proper volunteer hospital corps, (3) a nurse corps of selected trained women nurses ready to serve whenever necessity should arise, (4) a year's supply, for an army of at least four times the normal strength, of all medicines, hospital furniture, and stores as are not materially damaged by keeping, to be held constantly on hand in the medical supply depots, (5) charge of transportation to such in extent as will secure prompt shipment and ready delivery of all medical supplies, (6) simplification of administrative paper work, (7) provision for purchase by subsistence funds of articles of special diets for the sick.

O'Reilly and his staff achieved a relation with the army, with Congress, with the medical profession, and with the public never visualized by any previous administration.

Never of strong constitution and the subject of much ill health during his army career, his remaining three years were spent quietly in a state of semi-invalidism in Washington, where he died of uremic poisoning, on November 3, 1912.

This article includes text from the website Office of Medical History, which as a work of the United States federal government, is in the public domain.