Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/563

547 H Y D H Y D 547 &amp;gt;Q anticipated. The chief morbid changes which have been described are evidences of congestion and inflammatory action in certain portions of the brain and spinal cord, but more particularly in the locality known as the &quot; respiratory centre &quot; of the medulla oblongata, where the accumulation of &quot; leucocytes &quot; around the small blood-vessels and in the surrounding nervous substance are a prominent phenomenon. Similar changes have been found in the salivary glands. On the whole, however, it can scarcely be said that the formidable array of symptoms above narrated are accounted for by these appearances, which in the opinion of some are in all likelihood merely the results of antecedent processes of an occult nature affecting the nerve centres and forming the essence of the disease. That emotional disturbance is present is undeniable, for it is found that those cases of hydrophobia are less severe where there is no suspicion on the part of the sufferer of the nature of his complaint ; yet this only represents one of many elements. The function of the eighth pair of nerves (which are largely concerned in the processes of respiration and deglutition) is disturbed in a marked degree, and it is probable that this is the portion of the nervous system upon which the poison most powerfully exerts its specific action. But that the great nerve centres, viz., the brain and spinal cord as a whole, are profoundly affected, is manifest in the tendency to general convulsion, the remarkable hyperaesthesia, and the mental perturbation of the patient. The treatment of most avail in this disease is that which is directed towards preventing the absorption of the poison into the system. This may be accomplished by excision of the part involved in the bite of the rabid animal, or, where this from its locality is impracticable, in the appli cation to the wound of some chemical agent which will destroy the activity of the virus, such as potassa fusa, lunar caustic (nitrate of silver), or the actual cautery in the form of a red-hot wire. The part should be thoroughly acted on by these agents, no matter what amount of temporary suffering this may occasion. Such applications should be resorted to immediately after the bite has been inflicted, or as soon thereafter as possible. Further, even though many hours or days should elapse, these local remedies should still be applied ; for if, as appears probable, some at least of the virus remains for long at the injured part, the removal or effectual destruction of this may prevent the dread consequences of its absorption. Every effort should be made to tranquillize and reassure the patient. When once the symptoms of hydrophobia have declared themselves, little can be achieved by the resources of the physician beyond palliating the agonizing sufferings and rendering easier the inevitably fatal event. Medicines cannot be administered by the mouth, owing to the impossibility of swallowing and the distress occasioned by the effort to do so ; they must therefore be given either by the bowel in the form of enema, by hypodermic injection, or by inhalation. The most approved and potent agents are opium, belladonna, curara, chloral, and chluro- form inhalation. The vapour bath is also recommended. It need scarcely be said that those coming in contact with the patient should guard against the risk of being bitten during the paroxysms of excitement, or of being inoculated by the saliva, for although there are few if any well-authen ticated cases of the disease being communicated in this way, yet the possibility must be admitted. It should be remarked that occasionally an individual who may have at some time been bitten by a non-rabid dog manifests symptoms strongly resembling in many points those of hydrophobia. These are often simply the effect of fear, and have much of the hysterical element mixed up with them. They are generally of much less severity in every way than those of the true disease, and yield readily to treatment appropriate to the disturbed nervous condition. (j. o. A.) HYDKOZOA FT! HE HYDROZOA form one of the three classes into I which the Coelentera nematophora (distinguished from the Ccelentera porifera, or Sponges) have been divided, recognized as such in the article C(ELENTERA, to which the reader is referred. It results from observations made by Ernst Haeckel, since that article and the article ACTINOZOA were penned, that the CtenopJiora should not be regarded as a class equivalent to the Hydrozoa and Actinozoa, nor as a subdivision of the latter class, but that they must be con sidered as a peculiar modification of the medusiform Hydrozoa (see final paragraph). If this conclusion be accepted, it will be necessary to divide the Hydrozoa into two primary groups or grades, for which the names Polypo- morpha and Ctenophora are proposed. The Hydrozoa correspond to the Linnasan genera Hydra, Tubularia, Sertidaria, and Medusa. The name was applied by Huxley in 1856 to a group corresponding to that termed Hydromedusce by Vogt (1851) and Medusae by Leuckart (1853), and embracing the forms placed by Gegenbaur in his Elements of Comparative Anatomy (1878) in four classes, viz., Hydromedusce, Calycozoa, Thecomedusce, and Medusae. Our knowledge of the structure and life-history of the Hydrozoa, many of which, on account of their delicacy and oceanic habits, are excessively difficult to obtain in a state fit for investigation, has greatly extended within the last five years. Whilst in the two decades preceding this period the admirable researches of Huxley, Gegenbaur, Agassiz, and Allman had brought to light and systematized a vast mass of information with regard to these organisms, the later observations of Claus, the Hertwigs, Haeckel, and Metschnikoff, have corrected, extended, and added to their history, especially in respect of embryological and histological detail. An epitome of the present condition of our knowledge of the group is afforded by the subjoined tabular classification of its families, orders, and sub-classes. The definition and synonymy of the divisions recognized will be entered into, after a sketch has been given of the common structural features of typical Hydrozoa. CLASS HYDROZOA. Sub-Class I. Scyphomedusae (syn. Ephyromedusoe). Order 1. LUCERN-ARMS. Examples. ( Luceniaria (fig. 19) Fam. 1. Eletitherocarpida; | JLilidystus. ( Craterolophus. 2. CleistocarpidiE j Manama. Order 2. DISCOJIEDUSJE (Haeckel). Sub-Order 1. Cubostomse. Fam. 1. Protepliyridaj. ,, 2. Nausithoidos Nausithc. 3. EphyielHdK. 4. Atollidas. ,, 5. Cycloi cliidse. Sub-Order 2. Seinostomse. ( Chrysnora (fig. 24, 6) Fam. 1. Pelagido: } PelaRia., 2. Cyanrcidrc Cyauwa. , 3. Sr henonida; Sthenonla. ,, 4. Aurelidse Aurelia (figs. 36-31). Sub-Order 3. Rhizostomze. Fam. 1. Tetragamclioe Cassiopeia. ( Khizostoma (fig. 24, a). 2. Monogamelwj | Crambessa. Order 3. CONOMEPI;?^ (Haockel). Fam. 1. Cliarybdoidoe Charybdse* (fign. 20-23). 2. liursaridaj. 3. Chiropsalmidte. Order 4. PEROMEDUS.* (Haeckel). Fam. 1. Periphyllidse. 2. Pericryptidse.