The _pathology_ of the disease consists in an inflammation of the mucosa of the sinus, and the filling of that cavity with blood or, later, with a muco-purulent fluid, the escape of which is prevented by the closure of the nasal outlet by swelling. This of itself produces violent headache and much nervous disorder as witnessed by the drooping head, closed eyelids, prostration, high fever, anorexia, and in cows suppression of the milk secretion. But there is reason to believe that this is aggravated by the septic germs, which inspired with the air, were already present in the sinus, and which in the comparative absence of oxygen, in a rich culture medium and in contact with injured and debilitated tissues, assume an enhanced pathogenic rôle. This may serve to explain the ulceration of the mucosa of the sinus found in subjects that have suffered for some time. It further explains the notorious fact that the free access of air (oxygen) to the inflamed sinus is one of the most helpful therapeutic measures. _Symptoms of the Acute Form._ When the disease is traumatic the first symptom is usually a hæmorrhage from the nose, the blood being of a bright crimson. Respiration is hurried, and appetite diminished, yet rumination may be imperfectly performed. The bleeding may be repeated for days in succession, but the ox is still capable of work. On the fifth or sixth day there is complete anorexia, rumination ceases, the head sinks resting on the manger or soil, the ears droop forward and downward, and may be swollen. The head inclines to the affected side, the corresponding horn is intensely hot, and the eyes are closed. Light percussion of the forehead on the affected side gives pain, and the sound elicited is flat and dull as compared with that from the opposite side. The temperature of the body rises 2° or more, the pulse becomes frequent, full and hard and the impulse of the heart abnormally strong. Costiveness, partially suppressed and high colored urine, and dry hot muzzle betray the fever. Unless relieved the chronic form may supervene. SYMPTOMS OF THE CHRONIC FORM. When this comes on slowly, working oxen get emaciated, lose appetite, have the eyes dull and sunken, and the lids drooping, the coat rough and staring and the skin harsh, dry, and lacking in pliancy, the head is carried low when out of the yoke and, after shaking the head and sneezing, a glairy, slightly fœtid matter escapes from the nostril. The breath is fœtid and appears to be offensive to adjacent cattle. This may continue for months with no other change than a more constant nasal discharge, and increasing emaciation and weakness. _Prognosis._ This is favorable for the acute disease at the outset. But if no relief is furnished it is liable to go on to a fatal issue. Even the chronic form is curable unless the subject has already become hopelessly weak and debilitated.