It is observable that the two morbid conditions now described, that of excessive vascularity and that of increased secretion, are never co-existent. If the vessels of the brain and its membranes are loaded with blood, there is little or no fluid within the former or between the latter: if, on the contrary, the effusion be great, there is little or no appearance of vascularity. Effusion is the effect and the termination of vascularity; it is the ultimate result of vascular action, and the effect having ensued, the cause ceases to be apparent. The substance of the spinal cord is seldom changed, either in vascularity or in consistence: the morbid changes which this organ undergoes have hitherto been observed only in the membrane that invests it, which, as has been just stated, is not only highly vascular, but likewise contains a much larger quantity of fluid than natural. 3. _Morbid Appearances in the Thorax._ Of all the thoracic viscera, that which is most frequently diseased is the mucous membrane of the bronchi. The disease which takes place in this organ is not only the most constant, whatever be the type or the degree of fever, but it is also the most characteristic of the febrile state. Its disease is specific and uniform. It consists of preternatural redness. The character of this redness distinguishes it from that which is observed in ordinary inflammation. It is uniformly and strikingly darker, the difference in colour being precisely that which subsists between venous and arterial blood. This darkness of colour apparent in the bronchial lining, increases in degree as the tubes of the bronchi diminish in size: while it may be only just discernible in the large trunks, the colour may be nearly black in the minute branches. This change in the natural colour of the membrane is indicative, not only of an increase in its vascularity, but of alteration in its structure. It is almost always attended with a preternatural thickening of its substance, as is demonstrated by cutting through the tube and reflecting the membrane. The tubes themselves contain more or less fluid, which consists of mucus, mixed with pus. Analogous to what has been stated with regard to the vascularity of the brain and to its secretions, when the quantity of secretion contained in the bronchial tubes is great, the degree of vascularity apparent in the membrane is lessened.