Medical directors of the Army.Dr. Charles S. Tripler was General Mc-Clellan's first medical director. Although he had accomplished an immense amount of work, his machinery was not flexible enough to care for 100,000 men, and during the Peninsula campaign there was much confusion and an immense amount of suffering. But for the Sanitary Commission, which had charge of the hospital-boats near White House Landing and which cared for many thousands wounded and carried away hundreds, the distress might have been much greater. Dr. Jonathan Letterman became medical director of the Army of the Potomac July 1, 1862, succeeding Dr. Tripler. Dr. Letterman was a man of great ability; he organized the ambulance corps, improved the field-hospital service, and instituted a method of furnishing medical supplies by brigades instead of by regiments. Many of his innovations continued throughout the war. After the larger part of the Army of the Potomac had returned with General Pope, Dr. Letterman found much difficulty in again organizing it properly. He was successful, however, and the care of the wounded after Antietam marks a distinct advance on anything before this time. During the first year of the Civil War it became evident that many of the forms then in use, especially the report of sick and wounded, were highly defective and unsatisfactory when applied to the new and broader conditions of war; and on May 21, 1862, measures were taken by the surgeon-general to secure much more detailed information in regard to cases of illness and injury, and in respect to other matters of record controlled by the medical department. Some years after the Civil War, however, the mass of records in the surgeon-general's and other offices became so great as to bring about the organization of a record division to take them over and provide for their preservation and care. On these records is founded the national pension system.