Simpson left his mark in other departments besides those of the subject of his professorial chair and of anaesthesia. About ten years after the introduction of chloroform he turned his attention to the process of wound-healing--the repair of necessary wounds inflicted by surgeons in the course of their work--and although he was promptly told to go back to his midwifery, he worked persistently at the subject. In those days the subject was the most burning one in surgery and the methods employed to bring about successful results varied in different schools. The object of all methods was the same, viz., to obtain a healthy, clean, and sightly result after an operation; to leave the part which had been of necessity cut in a condition as nearly as possible approaching that in which it had been found, without the incidence of any of the too frequent grave complications. Surgeons did not recognise at first the power of nature to effect for them what they strove after; they thought to attain their object by compelling the tissues to heal as they desired by complicated applications, and many were the layers of ointments and masses of dressings heaped on wounds for this purpose. For a long time all efforts were directed to the discovery of some specific substance, the application of which would give the necessary impulse towards healing in the desired manner. Before Simpson's day it had been generally recognised that the cause--but its nature was quite undreamt of--of the trouble lay in the air surrounding the wound, and more dressings were piled on to keep out the air. But at the same time bleeding was arrested by tying the cut arteries with ligatures--chiefly silken--and these were left with long ends hanging out of the wound to work their way out by a process of ulceration, or irritation of the tissues until liberty was obtained. This process was practically incompatible with the ideal form of healing, known as healing by _first intention_, _i.e._, union without appreciable loss of substance or the formation of _pus_ or matter. So-called "surgical fever," secondary haemorrhage, and blood-poisoning were the frequent fatal results of operation wounds treated in this manner. Simpson and others thought to prevent these alarming diseases by devising other means of closing the arteries; thinking that if some method or material were used, which nature resented less, the wound would more readily close by first intention. In 1858 Simpson stated that he had for some time past been experimenting with substitutes for the ordinary silk and thread ligatures, and in the course of his experiments had made use of iron, silver, and platinum wires. In his usual way he hunted up old authorities, and found a record of both silver and gold threads having been experimentally used by bygone practitioners. He seems to have been pleased with his results, stating that he found the tissues much more tolerant of these metallic ligatures than they were