CATARACT. 



93 



the siege of Jerusalem, the Romans had 300 catapults 

 and 40 balisUe. The Romans did not carry all the 

 parts of these machines with them, but only the ropes 

 and fastenings, with the necessary tools; and the 

 soldiers built the catapults when they wanted them. 

 The terms catapult and balista were often used in- 

 discriminately ; and, in later times, the word catapult 

 went entirely out of use. Vegetius and Ammianus 

 Marcellinus never introduce it, mid employ balistce 

 to signify all machines throwing large arrows or 

 beams, and onager for those throwing stones. 



CATARACT. By this term two very different 

 diseases are designated by some writers, viz. the true 

 cataract, and atnaurosis , or gutta serena. By the 

 first of these terms, in its most common signification, 

 is understood opacity of the crystalline lens, or its 

 capsule, or both. By the second is meant a disease 

 of the retina, by which it is rendered unsusceptible 

 of the action of light. In cataract, the lens becomes 

 opaque, loses its transparency, and is no longer capa- 

 ble of transmitting the light. The causes of cataract 

 are numerous. Inflammation may produce it. Some- 

 times it is ascribed to a state of the vessels of the 

 part which prevents a proper nourishment of the 

 lens or its capsule. It is produced by various dis- 

 eases, such as gout, rheumatism, scrofula, and accom- 

 panies old age. Its earliest approach is marked by 

 a loss of the natural colour of the pupil; this becom- 

 ing turbid, or slightly grey. MUSCCE volitantes ac- 

 company this period. The opacity is not, at first, 

 over the whole crystalline, and, most frequently, first 

 attacks the centre portion ; this being turbid, and of 

 a greyish colour, while the surrounding portions re- 

 main transparent, and of the usual black colour. 

 While it exists in this degree only, the person can 

 see in an oblique direction. The colour of the pu- 

 pil is various ; mostly greyish-white or pearl-colour- 

 ed ; sometimes milk-white, or of a yellowish-grey ; 

 now and then of a greyish-brown, and even of a dark- 

 brown or dark-grey. The consistence of the lens 

 differs in different cases, being either hard, and even 

 horny, or very soft, as if dissolved. 



The treatment of cataract is by a surgical opera- 

 tion on the eye, and different operations have been 

 tried and recommended. They all consist in remov- 

 ing the diseased lens from its situation opposite the 

 transparent cornea. By one of these operations, the 

 cataract is depressed, removed downwards, and kept 

 from rising by the vitreous humour. This is called 

 couching. Another operation is extraction, and con- 

 sists in making an incision of the cornea, and of the 

 capsule of the lens, by which the lens may be brought 

 forward, and through the cut in the cornea. r lhe 

 third operation is by absorption. This consists in 

 wounding the capsule, breaking down the crystalline, 

 and bringing the fragments into the anterior cham- 

 ber of the eye, where they are exposed to the action 

 of the aqueous humour, and are, at length, absorbed. 

 This last operation lias the name keratonyxis applied 

 to it. The choice of the operation is determined by 

 the character of the cataract. After the operation, 

 the patient is to be kept from the light, and from all 

 means of irritation. Such medicines and such arti- 

 cles of food are to be prescribed as will most effectu- 

 ally prevent inflammation ; and should this occur, it 

 must be treated by such means, as are the most sure 

 to restrain or overcome it. 



Amaurosis is a disease of the optic nerv, and its 

 continuation, the retina. Its causes are numerous. 

 It may be occasioned by organic disease of the parts 

 referred to, by mechanical pressure upon the nerve, 

 by too powerful light, by long-continued use of the 

 eyes in too weak light, by rapid transition from dark- 

 ness to light, and, finally, by oKl age. Various other, 

 and sonu- more general causes may produceamaiiro- 



sis. Among these are wounds of the head, compres- 

 sion of the brain, fits of apoplexy, suppressed colds 

 in the head, habitual inebriety, vomiting, coughing, 

 sneezing, affections of the alimentary canal and some 

 of the neighbouring viscera the liver, for example. 

 According to the activity of these various causes, the 

 malady comes on suddenly or gradually. The pa- 

 tients are sometimes unable to bear the light, and^ 

 therefore, seek the darkness, where sparks and flames 

 frequently appear to their eyes. Objects sometimes 

 appear of different colours, or fluctuate, swim, andl 

 confuse themselves. At other times, the patients 

 begin to squint, suffer a severe pain in the ball of the 

 eye, and a straining above the eyebrows : finally, 

 they begin to see as if through a crape or fog, and 

 only in bright daylight can distinguish accurately: 

 black flakes and specks appear to hover before their 

 eyes. The greatest insensibility of the retina is often 

 opposite the centre of the cornea; but ultimately 

 the disease produces total blindness, the pupil losing 

 its motion, and becoming permanently dilated. Deep 

 in the eye a white speck is often visible, which as 

 traversed by veins. According to the different causes, 

 the malady is either easily cured or is incurable. Re- 

 gard is especially to be had to them in the selection 

 and use of remedies. 



CATARACT, in geography (from the Greek 

 x<zraux<ri). The English language has more words 

 than most European languages, to express different 

 degrees of rapid and sudden descent in streams of 

 water. The most general term is falls. A consider- 

 able declivity in the bed of a river produces rapids ; 

 when it runs down a precipice, it forms a cataract ; 

 and, if it fells from steep to steep, in successive cata- 

 racts, it is often called a cascade. In primary and 

 transition countries, rivers abound in rapids: they 

 also sometimes occur in secondary regions, but the 

 descent is always more gentle. In alluvial districts, 

 falls, of course, are very rare : they are almost al- 

 ways found in the passage of streams from the primi- 

 tive to the other formations : thus falls are found 

 where the alluvial formations, on Jhe coast of Ameri- 

 ca, bonier on the primitive formations ; but none are 

 found in the alluvion below. Rapids and cataracts 

 are often the greatest blessing to rugged countries, 

 since they furnish the cheapest means to move mas- 

 chines in manufactories, &c. In flat countries, as 

 Holland, the lower partttf Germany, and the West 

 Indies, people must resort to windmills, on account 

 of the want of falls. 



Many cataracts are remarkable for their sublimity ; 

 and the falls of Niagara surpass all others of the 

 known world in grandeur. The whole mass of water 

 which empties itself from the great inland seas of 

 North America is here compressed into a channel cf 

 three quarters of a mile in width, and plunges over 

 a precipice of 150 to 160 feet in height. The river, 

 more than a mile above the falls, is divided by Grand 

 and Navy islands, and has a gradual descent of fifty- 

 seven feet from this place. The banks preserve the 

 level of the country, and, in some parts, rise 100 feet 

 from the water : the whole stream is covered with 

 foam and waves. At the grand falls, the river is 

 three quarters of a mile broad, and the precipice 

 curves nearly in a semicircle, extending in the longest 

 line on the American or eastern side. An island, 

 called Goat island, divides the cataract into two prin- 

 cipal portions the American fell on the east, and 

 the Horse-shoe on the west, or Canada side. A small 

 portion of the fall on the American side is cut off by 

 a small island on the precipice : the rest descends in 

 one body almost perpendicularly, from a height of 

 164 feet, and 1000 feet in width. Both the fells oti 

 the American side are crossed by bridges. The 

 Horse-shoe fall is fourteen feet less in height, hut 



