After several years Mr. Boutwell severed his relations with Mr. Giles, and upon his admission to the Suffolk bar in January, 1862, on motion of the late Judge Josiah Gardner Abbott, he began active practice in Boston. His first jury case was before the late Judge Charles Allen, of Worcester, yet at that time he had never seen a jury trial from the opening to the close. Mr. Boutwell had scarcely entered upon his professional career when he was called to assume a most important place in national affairs, and one that was destined to keep him in close relations with the Federal Government at Washington for many years afterward. Among the historical events, originating in the Civil War, was the passage of the act "to provide internal revenue to support the government and to pay interest on the public debt," approved July 1, 1862. Mr. Boutwell organized the Office of Internal Revenue and was the first internal revenue commissioner, receiving his appointment while at Cairo in the service of the War Department. He arrived in Washington July 16, and entered upon his duties the following day. Within a few days the Secretary of the Treasury assigned him a single clerk, then a second, and afterward a third, and the clerical force was increased from time to time until at his resignation of the office of commissioner on March 3, 1863, it numbered 140 persons. To him is due its organization upon a basis which has more than fulfilled the most cherished hopes and expectations of those who conceived the idea and which has furnished from the first a valuable source of revenue for the government with little hardship or unnecessary friction among the people at large. The stamp tax took effect nominally on the 1st of October, 1862, less than two and one-half months after Mr. Boutwell entered upon his duties as commissioner, yet before he resigned, five months later, he had the office so well established, and its work so thoroughly organized throughout the United States, that its usefulness was assured and it has continued to the present time practically the same lines that he laid down. In July, 1863, three months after he retired from the office, he published a volume of 500 pages, entitled "A Manual of the Direct and Excise Tax System of the United States," which included the act itself, the forms and regulations established by him, his decisions and rulings, extracts from the correspondence of the office, and much other valuable information bearing on the subject. This work has ever been accepted as authority, and still forms the basis of the government of the internal revenue system.