Notwithstanding his aversion to anything like strife in medical politics, Marshall Hall took a prominent part in the formation of the British Medical Association, and was at once elected on its Council, and delivered the oration on Medical Reform in 1840. He was in his true place in every philanthropic scheme that needed medical advocacy. The open railway carriages were doomed when he denounced them as dangerous to health; inhuman flogging of soldiers was evidently condemned when he expounded the character of the injuries inflicted on the cutaneous nerves, and the decree of shock to the heart. He even wrote on the Higher Powers of Numbers, in the _Mechanics’ Magazine_, and took an interest in devising new forms of conjugation for Greek nouns and verbs. He strongly advocated a new Pharmacopœia, based on the decimal system. He suggested in a pamphlet as early as 1850 new works for the sewerage of the Thames, developing his ideas more elaborately in 1852 and 1856. Many of his views and plans have since been adopted: others must and will still be carried out if London is to be properly and healthily drained. It is not to be imagined that Hall was so absorbed in study and practice that he could not take recreation. No one enjoyed more than he the pleasure of travelling, the tonic of the open air, the change to the Continent, a tour to America; and he rigorously took these, and enjoyed himself with the _abandon_ of a child. His delight in splendid scenery was extreme; and he gratified his taste, in season, by tours extending very widely over Europe. His visit to America was specially undertaken in 1853 with the object of studying slavery by personal observation. In New York and other cities he gave lectures by request illustrative of his discoveries. From Quebec to New Orleans, and even the Havana, his fame had preceded him, and he was feted and listened to with as much ceremony and enthusiasm as his retiring nature could be prevailed upon to endure. At the Havana he lectured in French for two hours, and the medical students of the city visited him again and again, thirsting for information at first hand. Dr. and Mrs. Hall returned to England in April 1854; and very soon after he published his little volume on “The Two-fold Slavery of the United States.” The subject was one which most deeply interested Marshall Hall’s philosophical and religious mind; and it is significant of the depth of his philosophy that he was far-seeing enough to be certain that unprepared abolition would be far from a perfect boon for the slave, while yet he regarded the continuation of slavery as wicked and degrading, financially ruinous, and tending to generate wars. His remedies were first, education; second, the appointment of fair task-work; third, the privilege of over-work, to be paid for, and the payments accumulated till freedom could be purchased with the aid of proportionate additions by the Federal and States’ Governments.