The facts advanced to prove these principles have not, of course, the wide range, the distinct statistical exactness, of those which the further progress of sanitary science has now enabled people to bring forward; but it is very interesting to see how all further advance has been but a development of the principles brought forward in this 'Treatise on Fever,' just as it was itself but a development of those brought forward five years before. Hardly any investigations had yet been made, but the results which research would bring to light are here foreshadowed. Even the direction which such research would take is indicated, for we are told, at the end of the chapter which treats of the "Causes of Fever," that-- "Further inquiries are necessary--such as, whether the vegetable and animal poisons we have been considering be the _only_ true, exciting cause of fever;[8] by what means its general diffusion is effected; on what conditions its propagation depends; by what measures its extension may be checked and its power diminished or destroyed; what circumstances in the modes of life, in the habits of society, in the structure of houses, in the condition of the public streets and common sewers, in the state of the soil over large districts of the country as influenced by the mode of agriculture, drainage, and so on, favour or check the origin and propagation of this great curse of civilised, no less than of uncivilised, man." Not a mere article or book contained the result of such inquiries. They occupied the greater part of his life, and that of many others. Their outcome is the present state of sanitary knowledge. If some people think there was nothing new in the view of epidemics insisted on in this Treatise, they have only to see what was the common opinion at that time amongst medical men. A few shared the writer's opinions, but the majority of English physicians then certainly took quite the opposite view. When Asiatic cholera first broke out in 1831, it was of no avail that the physicians of Bengal had declared unanimously that "the attempt to prevent the introduction of cholera by a rigorous quarantine had always and utterly failed"; it was of no avail that the articles on "Quarantine Laws" had, six years before, urged the same truth; the London College of Physicians issued, notwithstanding, a notification that, wherever cholera appeared, the sick should be collected together in houses, which should be marked conspicuously _Sick_; and that, even after the sufferers had been removed, and the houses purified, _Caution_ should be marked on them. That the dead from cholera should be buried in separate ground; that food to be delivered at a house where any one was sick should be placed outside, and only taken in when the person who brought it had gone away; and that no one who had communicated with a cholera patient should, during twenty days after, communicate with the healthy.