In 1828 he published “Commentaries on Diseases of Females,” with graphic plates depicting conditions of parts such as the tongue, lips, nails, &c., which he first associated with various disorders of women. He continued his series of careful papers on subjects connected with blood-letting. His writings on these two subjects produced him a considerable portion of his early practice. Meantime Marshall Hall married, in 1829, and soon afterwards settled in Manchester Square, where he lived for twenty years. Desiring to become a Fellow of the Royal Society, he entered upon a special research on the circulation of the blood, the results of which he might communicate to the Society. After carefully inspecting under the microscope the blood-flow in the transparent parts of frogs, toads, newts, &c., he arrived at the conclusion that all the blood changes, and all nutrition and absorption by the material tissues are effected in the minute or capillary channels between the arteries and the veins. The paper founded upon this research was read before the Royal Society in 1831, but was refused a place in the “Philosophical Transactions;” yet an equally great man, Johannes Müller, the leading German physiologist, pronounced his paper one of extraordinary interest. It was separately published in 1832. The Royal Society, however, did not reject Marshall Hall’s next paper, “On the Inverse Ratio between Respiration and Irritability in the Animal Kingdom,” which has been pronounced “one of the most beautiful examples of widely extended observations, and previously disjointed facts, all brought together and rendered harmonious by the insight and genius of a master-mind.”[20] From the latter subject the investigator passed to that of hybernation, his views on which also found acceptance with the Royal Society. One feature in his experiments on this subject was an ingenious apparatus for ascertaining the temperature of the bat without disturbing its winter sleep. By this time Marshall Hall had quite a little menagerie in his house, of animals whose physiology he was investigating; mice, hedgehogs, bats, birds, snakes, frogs, toads, newts, fishes were in turn laid under contribution. Abhorring cruelty as utterly as a man could, he yet saw the absolute necessity of discovering in the first instance, by experiments on animals, truths which were of vital importance both to men and brutes. Mr. Henry Smith of Torrington Square was his diligent associate in these inquiries. Dr. Hall said of him: “I never knew a person so accurate in his information and so devoid of selfishness. His interest in my researches never flagged. He was true to his appointments as the clock itself.”