_Plethora with Arterial tension_ and all conditions contributing to this, as already set forth under causes must be allowed a prominent place in considering the nature of the disease. The blood globules in my experience are somewhat smaller than normal, implying the density of the plasma, and implying a direct influence on trophic and metabolic processes. Under these influences the congestion of the encephalic circulation, and notably of the rete mirabile, and a serous effusion, tend first to prostrate the nerve force, and second to render the other intracranial structures anæmic. The direct action of a _narcotic poison_, leucocytic or microbian, though as yet a hypothesis merely, has much in its favor, on considerations drawn from the observed immunity in particular buildings, the sudden prostration, the promptitude of certain recoveries and the favorable results of the iodine mammary injections. The presence of sugar in the urine, most abundantly in the worst cases, implies a profound disorder in glycogenic centres (medulla, liver), and primarily no doubt in the bulb. _Lesions._ These are exceedingly variable in successive cases. Congestion and effusion in the meninges, cerebral or spinal, in the rete mirabile and choroid plexus have been often noticed, and exceptionally clots of extravasated blood. In certain cases congestion and pink discoloration of portions of the brain substance (cerebral convolutions, bulb, ganglia) with marked puncta vasculosa, are found, while in others the greater part or the whole of the encephalon is anæmic. The puncta in such cases, large and dark, on the surface of the section, promptly enlarge until they may form distinct drops. In the _lungs_ areas of collapse, and of dark red congestion and infiltration are common, mostly as the result of the entrance of alimentary or medicinal matters into the bronchia owing to palsy of the pharynx. Such materials can be found in the bronchial tubes. The _third stomach_ and the _large intestine_ may be impacted, the contents more or less baked and glossy on the surface, and coincident congestions of the mucosa are not uncommon. In some instances, however, the contents are soft and pultaceous and the absence of mucous congestions is remarkable. The _womb_ rarely shows characters differing from the condition which is normal to the first few days after parturition. The _blackness and thickness of the blood_ has been noted by practically all observers. This is partly the result of its density, but doubtless also of the undetermined toxins which are operative in the disease. Yellowish _gelatinoid exudates_ have been found in the subdorsal and sublumbar regions, as well as the cranium and spinal canal. _Glucose_ appears to be constantly present in the urine, and in excess in the more violent and fatal cases: from 1.19 grm. per litre in slight cases to 41.8 grms. in a fatal one (Nocard). Albumen may be present, though probably only when local inflammation has supervened.