These most important matters received very little consideration, and although much has lately been done to shew their influence in the origin and propagation of disease; yet they are not regarded as so efficient in that respect as they ought to be, and the reason of it is, that the common application of atmospheric contagion to the explanation of the problem, by the vast majority of medical practitioners, puts a stop to the scrutiny which would detect their relation. The fact undoubtedly is, that, in respect to some diseases, little is known, among those intrusted with their treatment, of their causes. This situation of affairs is dangerous, and were physicians to adopt the extravagant measures, which the doctrine of atmospheric contagion suggests, there is a risk that, armed with weapons of so powerful a nature as our medicines are, and moreover, applied to so delicate and nicely strung a machine as the human body, their interference might become downright tampering, and dangerous in the extreme. But the blame does not lie so much with the present generation of practitioners. It is more the fault of the science than of its present professors. That doctrine has been taught them, as on established and well authenticated principle. They have too readily confided in the accuracy of their predecessors, and taken for ascertained, that which was only supposititious. Still the public injury is the same, be that as it may; and would the profession perform efficiently its important duties, and deserve that confidence so necessary for the full operation of the art, they would, without delay, inquire into the merits of this case, and turn to the investigation of the causes of disease, the many facts and principles, revealed by the late rapid progress of the sciences. For the judicious and efficient treatment of disease, a knowledge of its causes is necessary. The disorders being ascertained, the first consideration in reference to the treatment is the cause or causes, and according as the information partakes of certainty or uncertainty, so the propriety of the measures is sure or doubtful. Without a knowledge of the causes, sure or probable, our efforts are, in some cases, like random blows made in the dark, they may or may not strike the object. It is in general only when the causes are known, more or less, particularly, that medical treatment can be said to rest on a sure and philosophical basis, and to promise the full amount of benefit the art can afford. For many years the investigation of Atmospheric Contagion has occupied the Author, anxious only to ascertain its actual merits, and to be guided by the result, free of prejudice or bias.