After a few years learning the trade, he moved to Lowell, Massachusetts, where he was hired by the Locks and Canals Machine Shop. In 1849 he took the position of "job hand" at the Essex Machine Shop.
There he manufactured locomotive parts and he built up enough of a cash reserve that he was able to purchase a share of the Manchester Locomotive Works when it opened in 1853. Blood took over the shop superintendent position at Manchester in 1857 when the original superintendent, O. W. Bayley, left the company.
It was Blood's opinion that the locomotives that Manchester produced were too light for the future needs of the railroads. When he took over in 1857, he quickly instigated more substantial locomotive construction at the shop. Through succeeding years, Blood acquired greater principal in the company until he was the majority owner.
When the Manchester Locomotive Works on Canal Street began operating in 1855 it employed 300 men who could produce three engines a month. After a promising start in 1855-1856, the company began to founder. It closed its doors in 1858 due to the lingering effects of the international financial panic of 1857. At that time, Agent and Superintendent Aretas Blood leased the Locomotive Works facilities where he set up a general purpose machine shop, known as Blood's Shop.
It would take six long years before the Locomotive Works could get back on its feet. The economic slowdown continued for months on end and then, in April 1861, the Civil War began. Locomotive engines were sorely needed for the war effort, but none of the early orders came to the Manchester company. The Locomotive Works finally restarted production in 1863. The first engine off the line was completed and sold in June 1864. A total of nine were built that year, with four contracted by the United States government for its military railroad.
More orders started coming in, and in 1865 the company manufactured 17 engines, each weighing 60,000 pounds. That year the Locomotive Works acquired an iron foundry off Elm Street, south of the railroad station's freight depot. It was conveniently connected to the Locomotive Works by the railroad track that ran parallel to Canal Street.
The foundry operated two furnaces 24 hours a day, enabling the company to control costs and maintain quality by making all of its own castings. In 1873 alone the company used 3.5 million pounds of castings made in the foundry. That year the furnaces consumed 4,500 tons of coal and 1,000 cords of wood. By 1875 the Locomotive Works employed 700 men, and by the 1880s it had the capacity to produce 150 locomotives a year.
He was the moving force behind the growth and success of the Manchester Locomotive Works, one of the city's leading enterprises for several decades. He had provided gainful employment to hundreds, and was generous in sharing his good fortune with the needy of Manchester through his support of the Manchester Women's Aid and Relief Society and other local charities.