Thus, then, it is proved, that some causes, totally independent of atmospheric contagion, produce the first cases of an epidemic, or widely spread disease. Now, there is no evidence that these same causes are not operating upon those who visit the sick, and in absence of any facts to the contrary, and of the operation of an equally active and undoubted agent, there is justice in thinking it probable that they are acting, more especially if the self-same results are manifested—and this may, with safety, be done, even when direct testimony cannot be obtained—which is very seldom entirely the case. The causes of the disease being widely extended, and the visited patient being ill from the operation of forces shared in common with many, it is only fair to conclude that as relatives, attendants, and visitors are like the great mass of people thus operated upon—that they, _cæteris paribus_, are as likely to be affected with the prevalent disease, as those who are suffering were previous to its invasion. They do suffer, but not in general in a greater proportion than other persons having no communication, and similarly situated in other respects. It would be ample time to look for the operation of some other agency in addition to those commonly experienced, when the portion of the community, holding communication with the sick, is affected with disease in a greater proportion than that portion having none. Now, with a few exceptions, it is the result of much patient investigation, not only into the experience of others, but of many epidemics we have had the most ample means of noting, that, in general, in respect to diseases held to be propagated by atmospheric contagion, those who have communication with the sick, do not suffer in a greater proportion than those who keep apart, but remain in the sphere in which the agencies and circumstances are operating, which produced the first cases. These exceptions are— _1st_, The relations and inmates of the same house inhabited by one sick of fever. _2d_, Those receiving disease from actual contact with the palpable contagious matter, or by contactual contagion. _3d_, Those persons, through the operation of fear, and from depression of mind, affected with disease, as fever, cholera, &c. _4th_, The attendants in fever institutions, &c. These exceptions will meet with a little consideration, in order to shew in what manner, and wherefore, those persons are seized in greater proportion, and to prove that it is not in consequence of atmospheric contagion. This statement is important, and is made cautiously, and only after the most detailed examination, and unprejudiced weighing of evidence. The facts which have led to that conclusion might be detailed, but, as they would occupy much room, and perhaps prove uninteresting to the general reader, they will be withheld, however, to be produced, if any sufficient objections be made.