SENNA 



SENSATION 



315 



Cassia obovata. 



signed on 23d May 1493 a treaty between Charle 

 VIII. of France and the Emperor Maximilian 1 

 There still exist the ruins of an old royal castle 

 Pop. 7111. 



Senna is the dried leaflets of several species o 

 Cassia, various preparations of which are used in 

 medicine as purgatives. Two sorts are recognise< 

 in the British Pharmacopoeia viz. Alexandrian 

 senna and Tinnivelly senna. The Alexandrian 

 senna leaves are chiefly obtained from Cassia acuti 

 folia, while the Tinnivelly senna leaves are yieldec 

 by Cassia angustifolia. Alexandrian senna is 



chiefly grown 

 in Nubia am 

 Upper Egypt 

 and is im 

 ported in large 

 bales from 

 Alexand ria. 

 It is ofter 

 adul teratec 

 largely with 

 the flowers, 

 pods, and 

 leaves of Sole 

 no st e mm a 

 Argel. Tin- 

 nivelly or East 

 Indian senna 

 resembles 

 Alexandrian 

 senna in odour 

 and taste. The 

 leaflets are, 

 however, larger 

 and fi n e r, 

 'about 2 inches 

 long, lanceo- 

 late, acute, unequally oblique at the base, flexible, 

 entire, green, without any admixture.' The 

 rounder leaves of the C. obovata are also used in 

 medicine, and are sometimes mixed with the other 

 kinds. 



The active principle in senna is a glucoside, 

 which has been named cathartic acid, and which 

 is closely allied to chrysarobin and the purgative 

 principle in rhubarb; there are also other sub- 

 stances which impart to senna its peculiar odour 

 and taste, as well as a variety of sugar. The 

 different pharmaceutical preparations of senna act 

 as moderately active cathartics, but tend to cause 

 griping. To obviate this, and to disguise the 

 nauseous taste of the drug, they are all made up 

 with a number of carminative and flavouring 

 substances. The active principles in senna are 

 excreted in the urine, which is coloured a deep 

 yellow, and by the milk, which is rendered purga- 

 tive. The officinal preparations comprise the con- 

 fection of tenna ( dose 60 to 120 grains ), the i- 

 fusion of tenna (dose 1 to 2 fluid oz. ), the syrup of 

 tenna, (dose 1 to 4 fluid drachms), the tincture of 

 tenna (dose 2 to 8 fluid drachms), and the com- 

 pound mixture of senna or 'black draught' (dose 

 1 to 1J fluid oz. ). Compound liquorice powder 

 consists largely of senna. The dose of senna itself 

 is 10 to 30 grains. 



BLADDER SENNA ( Colutea ) is a genus of shrubs of 

 the natural order Legtiminosse, sub-order Papilio- 

 nacew, having pinnated leaves, red or yellow 

 flowers, and remarkably inflated ixxls, whence the 

 English name. One species (C. arborescens) is 

 common in shrubberies in Britain. It is a native 

 of the south of Europe, and is found on the ascent 

 of the crater of Mount Vesuvius almost the only 

 plant that exists there. 



Seminar (properly Sennar, sometimes also 

 Stnaar), a city of the Eastern Soudan, stands 



on the Blue Nile, about 160 miles SSE. of Khar- 

 toum. Pop. 8000. It is the chief town of a dis- 

 trict lying between the Blue and the White Nile, 

 which was made an Egyptian province in 1820 

 but fell to the Mahdi in 1884. An account of the 

 disastrous expedition of Hicks Pasha into this pro- 

 vince in 1883 will be found in Colonel the Hon. J. 

 Colborne's book, With Hicks Pasha in the Soudan 

 ( 1885), and in Major Wingate's Mahdiism and the 

 Egyjitian Sudan ( 1891 ). 



Sennacherib, an Assyrian king, son of Sargon, 

 reigned 702 to 68 i B.C. The chief events of his 

 reign are enumerated under Assyria (q.v.). He 

 was the originator of great public works, as the 

 embankment of the Tigris, the making of canals, 

 watercourses, and the erection of a gigantic palace 

 at Nineveh. 



Senonian. See CRETACEOUS SYSTEM. 



Sens, an old town of France, dept. Yonne, 

 stands on the right bank of the Yonne, 70 miles 

 by rail SE. of Paris, and is still surrounded with 

 its ancient walls. Its principal ornament is the 

 Gothic cathedral of St Stephen, built in 1122-68, 

 but restored twice or thrice since. It has splen- 

 did portals, fine stained glass, and two large 

 bells ; in its treasury are preserved the vestments 

 of Thomas H Becket. There are also the palace 

 and ancient public offices of the archbishop, and a 

 town museum. The chemist Thenard was born in 

 the place. Pop. (1891) 13,942. See Vaudin, Let 

 Pastes de la Senonie ( Paris, 1882). 



Sensation may be defined as the change in 

 consciousness which results from the transmission 

 of nervous impulses to the brain. Such impulses 

 may be generated within the nerves themselves 

 ibut only in diseased conditions), or may l>e pro- 

 duced by stimuli applied to such parts of the hotly 

 as are provided with nerves. Such nerves are 

 often styled sensory or afferent. It must be re- 

 membered, however, that afferent impulses are 

 constantly being carried to the brain from all parts 

 of the body, resulting in motor and other acts 

 lecessary to our life, without exciting any sensa- 

 .ion at all. It is through our sensations that we 

 ?ain our knowledge of the external world, and of 

 ,he state of our body. The means by which these 

 ire produced are the elaborate nervous mechanisms 

 leveloped in connection with the various senses of 

 imell, sight, hearing, taste, touch, temperature (or 

 icat and cold), pain or general sensibility, the 

 miscular sense, and those of hunger and thirst. 

 rVliile we have obtained a certain amount of know- 

 edge of the nature of a nervous impulse resulting 

 n muscular movement, the same cannot be said 

 if a sensory nervous impulse. We cannot measure 

 he rate of its transmission along the nerve ; we 

 lave absolutely no notion of the change, if it is 

 egitimate to employ such a term, by which a 

 ensory nervous impulse becomes transformed into 

 a sensation ; we as yet know imperfectly at what 

 >art of the brain this transformation takes place, 

 ir by what paths the sensory impulses travel 

 owards the brain. It has long been known, how- 

 ver, that if the posterior division of the bundle of 

 erve fibres constituting that part of the cerebrum 

 vhich is termed the internal capsule (see BRAIN) 

 s destroyed a complete loss of sensation on 

 .he opposite side of the body results. This has led 

 o the investigation of the posterior part of the 

 erebrum, to which these fibres more specially pass, 

 or 'centres,' the destruction of which would in- 

 olve loss of the various forms of sensibility. The 

 -nits are as yet conflicting. It is generally agreed 

 hat the ' centre ' for sight is in the inner side of the 

 ccipital lobe ; but there is in the angular con- 

 olution another centre in which visual sensations 

 robably undergo a further elaboration. Above the 



