“Among the middle and higher ranks of society in Chester and its neighbourhood, during a period of thirty-one years, I scarcely recollect a single instance of the typhus fever being communicated to a second person, not even during the epidemics of 1783 and 1786, which excited a general alarm in that city, Fresh air and cleanliness were the only means which I employed to prevent infection. Doors and windows were kept open as far as the season, and other circumstances, would permit. Curtains were drawn to exclude the light, but not the free circulation of air. All clothes, utensils, &c. used by the patient were immersed in a vessel of cold water immediately, and, when taken out of it, carefully washed. The floors were kept clean, and vinegar was sometimes, but not always, employed to sprinkle. It was thought to be more easy to remove than to correct the poison.” Dr Haygarth deserves much credit for his judicious treatment, and by it he had the satisfaction of seeing much public good effected. His principles are yet acted upon with the very best effects; but it will be shewn, at a more advanced part of this work, that the check put to the progress of disease, was rather to be attributed to the removal of an atmosphere loaded with unwholesome emanations, than to any power those steps or measures had, of rendering innocuous, by dilution, a specific contagious poison. Dr Haygarth continues—“The whole evidence which I have been able to collect, incontestibly leads to this very important conclusion, that febrile infection extends but to a very narrow sphere from the person. “It appears highly improbable that the typhus infection should ever be communicated in the open air, by the common intercourse of society; because visitors, and even attendants, with very few exceptions, escape the fever, when exposed to it, in even the same chamber, if clean, airy, and spacious. “The quantity of miasms (unwholesome or poisonous air) respired in the latter, is incomparably more than it can be in the former situation. It is not, however, intended to be asserted that such an event is impossible, if a person on purpose, or by some rare accident, were to breathe the air which immediately issues from a patient, or from clothes fully impregnated with the poison. “During my long attention to this inquiry, not a single instance ever occurred to prove that persons liable to the small-pox could associate in the same chamber with a patient in the distemper, without receiving the infection. “We have no certain knowledge in what manner infectious fevers are received into the body. According to the most plausible conjecture they appear to be communicated by poisonous vapours, which issue from the breath, or the insensible perspiration, or the excretions of a patient in the distemper. These miasms are probably taken into the body by the absorbents of the mouth, nostrils, lungs, stomach, or skin.”