, KENIIKDEN, Atom menhaden, a fish of the same genus with the shad (q.v.), which is caught in great quantities on the coasts of New York and New England during the summer months, when it visits them for the purpose of spawning. Its length is from 8 either difficult or impossible, and therefore the name meningitis is most applicable to, either or both. Inflammation of the cerebral meninges is called cerebral meningitis, and. that of the spinal meninges, spinal meningitis. When the membranes of both brain and. cord are involved, the affection is called cerebro-spinal tneningitis. Inflammation of the substance of the brain is cerebritis, while inflammation of the spinal cord is myelitis (q.v.). Meningitis may be arranged under the following heads : 1. Inflammation of the dura mater, or pachymeningitis. 2. Cerebral meningitis, acute and chronic, including rheu inatic meningitis. 3. Tubercular meningitis. 4. Spinal meningitis, acute and chronic. 5. Cerebro-spival meningitis. 1. Inflammation of the dura-mater, or pachymeningitis (so called because it is inflammation of the thick, tough membrane, the dura-mater), was first described by Virchow under the latter title, and also, in some cases, under that of hema toma of the dura-mater. The inflammation may be on the outer surface of the dura-ma ter next the osseous. substance, but this form is of rare occurrence, and never takes place except from injuries or osseous growths; it is to the affection attacking the inner surface. 'of the dura-mater—that covered by the outer layer of the arachnoid membrane—to. which attention is here called. A principal characteristic is the formation of adventi tious membranesovhich appear to be repetitions of the arachnoid, resembling it in its, spider-web structure, not being false membrane, but having blood-vessels, which after a while rupture and cause extravasation of blood, which collects in cysts, thus constitut ing the peculiar form called hematoma of the dura-mater. In some cases there are as. nniny as twenty layers of membrane. The extent covered by these cysts varies. They are generally oval, four or five inches long and a half au inch or more in thickness, containing from one ounce to sometimes more than a pound of blood. The brain beneath is, of course, compressed, anmic, and often softened. The symptoms are, primarily, those of inflammation, and secondarily, those of pressure. The diagnosis is exceeding ly difficult, and the terinination is usually fatal. 2. Cerebral meningitis. Acute cerebral
meningitis is not of very comnaon occurrence, but nevertheless of great importance. The. inflammation is of the same character as that which attacks other serous membranes- redness, with serum, coagulated famine or lymph, and pus; but these products are beneath, and not upon the surface of the arachnoid; in other words, they are deposited in. the meshes of the pia-mater. Generally both hemispheres are involved, constituting what is called a bi-lateral affection. Post mortem examination often discloses thc existence of serum beneath the arachnoid, but this may follow atrophy or anxmia. The condition. most to be relied on is lymph, in sufficient quantity te be seen, or pus. The affection, may be caused by injuries to the head, sometimes by expostire to the sun. Indulgence in spirituous liquors is not an infrequent cause. Acute cerebral meningitis sometimes. occurs in connection with acute rheumatism of the joint,s, and ia then called rheumatic: meningitis and cerebral rheumatism; and it is regarded as being produced by the same. causes which produce arthritic rheumatism. Acute meningitis may be mistaken for. cerebral congestion, and after recovery incases where the disease has not passed into the second stage, that of compression, it is often impossible to be certain as to what the affection.has been, congestion or inflammation. Typhoid fever has been mistaken for meningitis, when there has been much delirium, but the presence of diarrhea, tender ness and gurgling on pressure in the right iliac region in typhoid fever, and the continu ance of delirium in the latter affection, are sufficient to mark the distinction. Acute mania has some symptom.s like those of acute meningitis, but there is not that morbid acuteness of the senses; moreover, in mania, fever and the symptoms of compression do.' not follow the delirium. Acute meningitis is a very dangerous disease, some cases end ing fatally in 36 hours; but the fatal cases rarely extend beyond 9 days. The most unfavorable symptoms are 'coma (q.v.), difficulty of swallowing, feebleness of pulse, and want of nervous sensibility (anaesthesia). Recovery- frequently takes place after there has been strabismus (see Squrtrixo, ante), paralysis, and convulsions, but as a rule 'more than half of the cases terminate fatally.