Five years more of daily experience and constant thought passed before his 'Treatise on Fever' was published.[6] It entered fully into all the phenomena of the disease and into the question of its treatment. It added largely to the knowledge of fever existing at that time, and was welcomed by the medical profession. 'The Medico-Chirurgical Review,' the highest authority of that day, pronounced it to be "the best work on Fever that ever flowed from the pen of physician in any age or country." It was for a long time the standard work on the subject with which it dealt. The most important part of the work, however, as might be expected, is that which relates, not to the treatment of disease (which has since his time much changed) but to its _causes_. And here we find an elaboration of the principles laid down five years before in his articles in the 'Westminster Review.' Those articles had been the result of a rapid glance which had gone to the very root of things, though when they were written their writer had held his position at the Fever Hospital for one year only, and had therefore not acquired the large experience of fever which he subsequently attained. But the five years that had passed since they were written could not change--could only strengthen--his conviction of the truth of the principles which he had previously expounded. In the 'Treatise on Fever,' as in the articles just quoted, it is enforced upon us, that since epidemics are everywhere the same, when they reach our own country we must expect to find conditions similar to those which produce pestilence in foreign countries. He writes as follows:-- "_The room of a fever patient, in a small and heated apartment of London, with no perflation of fresh air, is perfectly analogous to a stagnant pool in Ethiopia full of the bodies of dead locusts. The poison generated in both cases is the same; the difference is merely in the degree of its potency. Nature with her burning sun, her stilled and pent-up wind, her stagnant and teeming marsh, manufactures plague on a large and fearful scale. Poverty in her hut, covered with her rags, surrounded by her filth, striving with all her might to keep out the pure air and to increase the heat, imitates Nature but too successfully; the process and the product are the same, the only difference is in the magnitude of the result. Penury and ignorance can thus, at any time and in any place, create a mortal plague._"[7] Dr Southwood Smith has been accused of ignoring the fact that those suffering from fever can communicate the disease to others--of "infection," as it is called. But he did not. He shows, on the contrary, that the atmosphere of a room such as that spoken of in the passage just quoted must have the power of inducing fever in others besides the patient. He even says that "the poison formed by the exhalations given off from the living bodies of those affected by fever is by far the most potent febrile poison derived from animal origin."