The consequences of embolism vary with the character of the embolus and its situation. A simple plug of fibrine in a vessel only produces changes in the circulation, but a plug from a gangrenous thrombus has a tendency to excite suppurative inflammation wherever it lodges. The size of the artery thus obstructed, and the character of its collateral circulation also lead to a variety of results. If a large artery is stopped, the part becomes empty; if a small one the part may become extravasated with blood from the collateral circulation. Thus, if the large arteries supplying the extremities are obstructed, paralysis of the muscles, and finally dry gangrene, ensue. Emboli of the pulmonary arteries produce sudden death; of the coronary arteries, sudden death; of the cerebral arteries, softening of the brain; of the retina, sudden blindness; of the mesenteric arteries, congestion and gangrene of the intestines. Abscesses are also produced. This takes place when the embolus is of an irritative and gangrenous nature. Large abscesses are only found in the lungs and liver, therefore the mechanical results of an embolus produce the following condition of affairs: A set of vessels are first emptied of their blood, and the nutrition of their walls thus impaired; after a time these vessels are filled up from the veins, their abnormal walls can no longer resist the blood pressure, and hemorrhage takes place. After an hemorrhagic infraction is formed, the subsequent changes are of a degenerative character. The blood loses its coloring matter and breaks down into a mass of granules, forming a dry, yellow, wedge-shaped mass, or it may break down and form into a puriform fluid, or it may be surrounded by a zone of inflammation or of gangrene. The above condition of the system will explain why and under the circumstances enumerated, the injection of a blood vessel may be brought to a sudden stop without any apparent cause, and the injecting fluid flow back towards the injecting point. The various causes for such a result have been clearly demonstrated, but with the knowledge of these causes as previous stated, the remedy can be applied without much trouble. It can be estimated by the amount of fluid injected, about to what extent the vessel has been filled, and by following its course the point where the obstruction is, can be easily ascertained. By reopening the vessel at a point above, the injection may still be carried on successfully, or the corresponding vessel on the other side of the body may be used for that purpose. It is then that even a limited amount of knowledge of anatomy of the human body will be found of immense advantage to the operator, inasmuch as it will trace the cause of action, to be followed in this case, and will enable him to do so with success.