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Rh antagonizes half a grain of pilocarpine. The circulation is depressed by the drug, the pulse being slowed and the blood pressure falling. The cardiac action is due to stimulation of the vagus, but the dilatation of the blood-vessels does not appear to be due to a specific action upon them. The drug does not kill by its action on the heart. Its dangerous action is upon the bronchial secretion, which is greatly increased. Pilocarpine is not only the most powerful sialogogue but also the most powerful diaphoretic known. One dose may cause the flow of nearly a pint of sweat in an hour. The action is due, as in the case of the salivation, to stimulation of the terminals of the sudorific nerves. According to K. Binz there is also in both cases an action on the medullary centres for these secretions. Just as the saliva is a true secretion containing a high proportion of ptyalin and salts, and is not a mere transudation of water, so the perspiration is found to contain a high ratio of urea and chlorides. The great diaphoresis and the depression of the circulation usually cause a fall in temperature of about 2° F. The drug is excreted unchanged in the urine. It is a mild diuretic. When given internally or applied locally to the eye it powerfully stimulates the terminals of the oculomotor nerves in the iris and ciliary muscle, causing extreme contraction of the pupil and spasm of accommodation. The tension of the eyeball is at first raised but afterwards lowered.

The chief therapeutic use of the drug is as a diaphoretic in chronic Bright’s disease. It is also used to aid the growth of the hair—in which it is sometimes successful; in cases of inordinate thirst, when one-tenth of a grain with a little bismuth held in the mouth may be of much value; in cases of lead and mercury poisoning, where it aids the elimination of the poison in the secretions; as a galactagogue; and in cases of atropine poisoning (though here it is of doubtful value).

JACA, a city of northern Spain, in the province of Huesca, 114 m. by rail N. by W. of Saragossa, on the left bank of the river Aragon, and among the southern slopes of the Pyrenees, 2380 ft. above the sea. Pop. (1900), 4934. Jaca is an episcopal see, and was formerly the capital of the Aragonese county of Sobrarbe. Its massive Gothic cathedral dates at least from the 11th century, and possibly from the 9th. The city derives some importance from its position on the ancient frontier road from Saragossa to Pau. In August 1904 the French and Spanish governments agreed to supplement this trade-route by building a railway from Oloron in the Basses Pyrénées to Jaca. Various frontier defence works were constructed in the neighbourhood at the close of the 19th century.

The origin of the city is unknown. The Jaccetani ( ) are mentioned as one of the most celebrated of the numerous small tribes inhabiting the basin of the Ebro by Strabo, who adds that their territory was the theatre of the wars which took place in the 1st century between Sertorius and Pompey. They are probably identical with the Lacetani of Livy (xxi. 60, 61) and Caesar (B.C. i. 60). Early in the 8th century Jaca fell into the possession of the Moors, by whose writers it is referred to under the name of Dyaka as one of the chief places in the province of Sarkosta (Saragossa). The date of its reconquest is uncertain, but it must have been before the time of Ramiro I. of Aragon (1035–1063), who gave it the title of “city,” and in 1063 held within its walls a council, which, inasmuch as the people were called in to sanction its decrees, is regarded as of great importance in the history of the parliamentary institutions of the Peninsula. In 1705 Jaca supported King Philip V. from whom, in consequence, it received the title of muy noble, muy leal y vencedora, “most noble, most loyal and victorious.” During the Peninsular War it surrendered to the French in 1809, and was recaptured in 1814.

 JACAMAR, a word formed by Brisson from Jacameri, the Brazilian name of a bird, as given by Marcgrave, and since adopted in most European tongues for the species to which it was first applied and others allied to it, forming the family Galbulidae of ornithologists, the precise position of which is uncertain, since the best authorities differ. All will agree that the jacamars belong to the great heterogeneous group called by Nitzsch Picariae, but further into detail it is hardly safe to go. The Galbulidae have zygodactylous or pair-toed feet, like the Cuculidae, Bucconidae and Picidae, they also resemble both the latter in laying glossy white eggs, but in this respect they bear the same resemblance to the Momotidae, Alcedinidae, Meropidae and some other groups, to which affinity has been claimed for them. In the opinion of Sclater (A Monograph of the Jacamars and Puff-birds) the jacamars form two groups—one consisting of the single genus and species Jacamerops aureus (J. grandis of most authors), and the other including all the rest, viz. Urogalba with two species, Galbula with nine, Brachygalba with five, and Jacamaralcyon and Galbalcyrhynchus with one each. They are all rather small birds, the largest known being little over 10 in. in length, with long and sharply pointed bills, and the plumage more or less resplendent with golden or bronze reflections, but at the same time comparatively soft. Jacamaralcyon tridactyla differs from all the rest in possessing but three toes (as its name indicates), on each foot, the hallux being deficient. With the exception of Galbula melanogenia, which is found also in Central America and southern Mexico, all the jacamars inhabit the tropical portions of South America eastward of the Andes, Galbula ruficauda, however, extending its range to the islands of Trinidad and Tobago. Very little is known of the habits of any of the species. They are seen sitting motionless on trees, sometimes solitarily, at other times in companies, whence they suddenly dart off at any passing insect, catch it on the wing, and return to their perch. Of their nidification almost nothing has been recorded, but the species occurring in Tobago is said by Kirk to make its nest in marl-banks, digging a hole about an inch and a half in diameter and some 18 in. deep.

 JAÇANÁ, the Brazilian name, according to Marcgrave, of certain birds, since found to have some allies in other parts of the world, which are also very generally called by the same appellation. They have been most frequently classed with the water-hens or rails (Rallidae), but are now recognized by many systematists as forming a separate family, Parridae, whose leaning seems to be rather towards the Limicolae, as apparently first suggested by Blyth, a view which is supported by the osteological observations of Parker (Proc. Zool. Society, 1863, p. 513), though denied by A. Milne-Edwards (Ois. foss. de la France, ii. p. 110). The most obvious characteristic of this group of birds is the extraordinary length of their toes and claws, whereby they are enabled to walk with ease over water-lilies and other aquatic plants growing in rivers and lakes. The family has been divided into four genera—of which Parra, as now restricted, inhabits South America; Metopidius, hardly differing from it, has representatives in Africa, Madagascar and the Indian region; Hydralector, also very nearly allied to Parra, belongs to the