But although we cannot in cholera, more than in periodic fever, ascertain the _essential_ cause, there is no difficulty in showing the accidental auxiliary agents, which both in disposing to, and co-operating with it, give it much of its prevalence, and most of its fatal power. They consist in whatever deranges healthy action, and impairs constitutional vigour—such as unwholesome insufficient or irregular supplies of food—over labour—crowded and defective ventilation—dissolute habits, including vicious indulgences in intoxicating drink, and want of personal and domestic cleanliness—apprehension, anxiety, and inordinate emotions of the mind; and defective drainage, including sewerage, with resulting accumulation of organic matters. For the last, at least, the State and the authorities acting under it ought to be held responsible. Whether the last named agent—defective drainage and its consequences—constitutes any thing positive to the _essential_ cause of the disease, or is necessarily connected with it, or whether it only co-operates with those specified before it, in lowering the standard of health, by the production in excess of hydrogen and other gases, injurious to life, and thereby predisposes the body, through augmented susceptibility, for the action of the _essential_ cause cannot be determined. It is pretty certain, however, that neither it in any quantity, nor any amount of the other agents classed with it, as disposing and co-operating powers, in the production and extension of cholera, can of themselves create it. If they could, not only part of Ireland, but of places nearer home, must have been decimated, some of them depopulated. Whether excess or deficiency in the electric element, or disturbance in its ordinary relations, in the place where cholera appears, acts any part in the production of the disease, is not known. It seems probable that there is something abnormal in its distribution and movements; but that is all that can ever be reasonably conjectured, at least for the present, respecting it. Whether there is any affinity between the _essential_ cause of cholera and periodic fever, and, if any, of what kind, are questions that naturally suggest themselves in investigating the etiology of the former. That the question, as far as it relates to a certain affinity in the two cases, should be answered affirmatively, the following considerations seem to shew. Swampy undrained soils, the banks of rivers, the margins of harbours, and other low lying localities, with places where organic remains are artificially accumulated, or allowed to accumulate, prove the most prolific positions in the production of cholera, as well as of periodic fever. Both before the outbreak of cholera, and on its subsidence, fever of type, more or less distinctly marked, with predominance of gastric symptoms, are more frequent than usual.