I shall here refer the reader to the principles laid down in the outlines of the theory of fever, for an account of the manner in which the system was predisposed to this disease, by the debility induced by the reduction of its excitement, by action and abstraction, and by subsequent depression. Where a predisposition was thus produced, the fever was excited by the following causes, acting directly or indirectly upon the system. Where this predisposition did not exist, the exciting causes produced both the predisposition and the disease. They were, 1. _Great labour_, or exercises of body or mind, in walking, riding, watching, or the like. It was labour which excited the disease so universally among the lower class of people. A long walk often induced it. Few escaped it after a day, or even a few hours spent in gunning. A hard trotting horse brought it on two of my patients. Perhaps riding on horseback, and in the sun, was the exciting cause of the disease in most of the citizens and strangers who were affected by it in their flight from the city. A fall excited it in a girl, and a stroke upon the head excited it in a young man who came under my care. Many people were seized with the disease in consequence of their exertions on the night of the 7th of September, in extinguishing the fire which consumed Mr. Dobson's printing-office, and even the less violent exercise of working the fire engines, for the purpose of laying the dust in the streets, added frequently to the number of the sick. 2. _Heat_, from every cause, but more especially the heat of the sun, was a very common exciting cause of the disease. The register of the weather during the latter end of August, the whole of September, and the first two weeks in October will show how much the heat of the sun must have contributed to excite the disease, more especially among labouring people. The heat of common fires likewise became a frequent cause of the activity of the miasmata where they had been received into the body; hence the greater mortality of the disease among bakers, blacksmiths, and hatters than among any other class of people. 3. _Intemperance_ in eating or drinking. A plentiful meal, and a few extra glasses of wine seldom failed of exciting the fever. But where the body was strongly impregnated with the seeds of the disease, even the smallest deviation from the customary stimulus of diet, in respect to quality or quantity, roused them into action. A supper of twelve oysters in one, and of but three in another, of my patients produced the disease. Half an ounce of meat excited it in a lady who had lived, by my advice, for two weeks upon milk and vegetables, and even a supper of sallad, dressed after the French fashion, excited it in one of Dr. Mease's patients.