Both decaying and putrefying matters are capable of communicating their own state of putrefaction or of decay to any organic matter with which they may come in contact. To take the simplest case, a piece of decayed wood, a decaying orange, or a piece of tainted flesh is capable of causing similar decay or putrefaction in another piece of wood, orange, or flesh. In a similar manner the decaying gases evolved from sewers occasion the putrescence of meat or of vegetables hung in the vicinity of the place from which they escape. But this communication of putrefaction is not confined to dead matter. When tainted meat or putrescent blood-puddings are taken as food, their state of putrefaction is frequently communicated to the bodies of the persons who have used them as food. A disease analogous to rot ensues, and generally terminates fatally. Happily this disease is little known among us, but it is of very frequent occurrence in Germany. The decay or putrefaction communicated by putrid gases or by decaying matters does not always assume one form, but varies according to the organs to which their peculiar state is imparted. If communicated to the blood it might possibly happen that fever may arise; if to the intestines, dysentery or diarrhœa might result; and I think it might even be a question worthy of consideration, whether consumption may not arise from such exposure. Certainly it seems to do so among cattle. The men who are employed in cleaning out drains are very liable to the attacks of dysentery and of diarrhœa; and I recollect instances of similar diseases occurring among some fellow-students, when I attended the dissecting-rooms. The effects produced by decaying emanations will vary according to the state of putrefaction or decay in which these emanations are, as well as according to their intensity and concentration. Thus it occurs frequently that persons susceptible to contagion may be in the vicinity of a fever patient without acquiring the disease. I know one celebrated medical man who attends his own patients in fever without danger, but who has never been able to take charge of the fever-wards in an infirmary, from the circumstance of his being unable to resist the influence of the contagion under such circumstances. This gentleman has had fever several times. This shows that the contagion of fever requires a certain degree of _concentration_ before it is able to produce its immediate effects. A knowledge of this circumstance has induced several infirmaries (the Bristol infirmary, for example) to abolish altogether fever-wards and to scatter the fever cases indiscriminately through the medical wards. Owing to this distribution, cases in which fever is communicated to other patients or nurses in the infirmary are very unfrequent, although they are far from being so in those hospitals where the fever cases are grouped together.