It was towards the end of his career, when the old Edinburgh Infirmary stood condemned, and various proposals for rebuilding it on a new site and improved plan were under discussion, that his voice was most loudly heard. For many years he had thought and taught that the great mortality after operations in hospitals was due to the impure state of the air therein, derived from the congregation of a large number of sick persons under one roof. He picturesquely stated that the man laid on a hospital operating table was exposed to more chances of death than the English soldier was on the field of Waterloo. His original suggestion was that hospitals might be changed from being crowded palaces, with a layer of sick on each floor, into villages or cottages, with one, or at most two, patients in each room; the building to be of iron, so that it could be periodically taken down and reconstructed, and presumably thoroughly renovated. This drastic proposal brings nowadays a smile to the lips, for we see now how he was groping in the dark; but the magnitude of it is but the shadow of the evil it was designed to cure. The change was so great as to be impracticable in the eyes of most men; he, on the other hand, contended that it was to be of incalculable benefit to humanity, and, therefore, no difficulty, however great, should be allowed to stand in the way. He did not understand that the evils arose not from the air itself but from what was in the air, known to us now as the micro-organisms. His remedy was a proposal to run away from the evils without receiving any guarantee that they could not and would not successfully pursue. Had Lister not arisen, Simpson's proposals might have possibly prevailed, for he laboured with all his persistent energy. The general belief of the profession--but it was no more than a belief--was that operations performed in country practice were not so frightfully fatal as those performed in town hospitals. This was Simpson's opinion, and he determined to test its truth by appeal to facts. He drew up a circular with a schedule for the insertion of results in a statistical form, and sent it far and wide amongst country practitioners. He awaited the result with anxious expectation; the circular asked for a plain statement of facts only, and for all he knew the facts might be against his theory; but they were not. From all over England and Scotland, particularly from mining districts, where severe operations after accidents were common, the filled-up schedules flowed in, to the number of 374. These were collected, carefully classified and summarised. The operations selected were amputations, and the result briefly was this:-- Total number of cases 2,098 } Mortality, " " deaths 226 } 10.8 per cent. The relative mortality of the different amputations was also shown:--