801 



HYPERBOLE. 



HYPOCHONDRIASIS. 



802 



the same abscissa c N, the tangents at r, p', &c., will all meet the axis 

 c A in the same point T : and any two such ordinates P N, p' N, will 



always be to one another in the proportion of the minor axes of the 

 hyperbolas to which they belong. 



If it were not necessary to consider the hyperbola in connexion with 

 the ellipse, perhaps the following way of describing it would be tha 

 most simple. 



Let c A be the semi-axis major, and c u one of the asymptotes : and 

 while the line K c moves parallel to A v, let p move upon that line in 

 such a way that the square on N P shall always be less than the square 

 on N u by the square on A v. Then P will trace out one branch of the 

 hyperbola. But if at the same time the square on R N exceed the square 

 on N u by the square on A v, the point B will trace out a branch of the 

 conjugate hyperbola. 



For a remarkable property of the area of an hyperbola see LOGA- 

 RITHMS. 



Among ellipses there is one sort which is conspicuous, namely 

 the ellipse in which the major and minor axes are equal, or the 

 circle. The corresponding hyperbola, namely, that in which the 

 major and minor axes are equal, is called the equilateral hyper- 

 bola; and though not so remarkable a curve as the circle 

 yet presents some peculiar simplification of properties. Iti 

 asymptotes are at right angles to one another, and the hyperbola ant 

 ita conjugate are similar and equal. Any semidiameter c P is equal to 

 ita semicon jugate c D, and r D ia at right angles to c w. Ita excentricity 

 ia \'2 or M142 . . . . , and the square on c N always exceeds the 

 square on N P by the square on c A. 



In the preceding article it will be observed that we have called the 

 two branches passing through A and M one hyperbola. They are 

 frequently called two opposite hyperbolas ; but they form in fact onl; 

 one curve, denned by one equation. 



HYPERBOLE (uirfp&o\-fi, from inrip above, 0dM.w to throw) means 

 literally an over-casting; in ita common sense, a going beyond the 

 truth in describing an object, not by the introduction of qualitief 

 which do not belong to it, but by the exaggeration of those which do 

 For example, it may be hyperbolical to say that the complexion of a 

 fair woman is whiter than snow ; but to say so of a brown woman is 

 either irony or simple falsehood. Poets in all nations have affecte< 

 this mode of speech ; but it ia peculiarly characteristic of the Orienta 

 nations, both in prose and verse. 



H YPERBOLOID. [SURFACES OP SECOKD DEGREE.] 



HYPERION, a Titan, the son of Uranus and Ge, and father o 

 Selene, Eos, and Helios, who is often called Hyperion. [HELIOS.] 



HYPEHSPIROILIC ACID. [SALICYLIC ACID.] 



HYPERTROPHY (from intif, above, and rpo^, nutrition), a term 

 in medicine signifying the enlargement of a part of the body from 

 excessive nutrition. The hypertrophied organ contains no new solit 



AKT3 A9D SCI. DIV. VOL. IV. 



r fluid substance, but one or more of its proper component tissues are 

 in greater quantity than in the healthy state. The opposite condition 

 if a part namely, diminished bulk from defective nutrition is termed 

 trophy. [ATROPHY.] 



When hypertrophy attains such a degree as to interfere with the 

 lotion of the organ in which it is seated, it constitutes an important 

 ind highly dangerous disease ; such is frequently hypertrophy of the 

 .eart. [HEART, DISEASES OF.] 



The immediate cause of the hypertrophied state is, as we have said, 

 ncreased nutritive action in the organ or tissue ; and since all parts of 

 he body are formed and nourished from the blood circulating in them, 

 t is natural to suppose that the production of hypertrophy would be 

 accompanied by increase of the quantity of that nutritive fluid in the 

 art. It is necessary, however, not merely that the blood should be 

 ollected in it in larger quantity, but also that it should circulate 

 rapidly through the minute vessels, so as to bring constantly fresh 

 >ortions of new nutritive matter into contact with the smallest com- 

 wnent particles of the structure. This is illustrated by reference to 

 .he known exciting causes of hypertrophy which give rise primarily to 

 this increased quantity and accelerated circulation of blood in the 

 small blood-vessels. There are, it is true, instances of hypertrophy of 

 which we cannot perceive any exciting cause : thus, in some persons 

 ,he adipose tissue, or fat, in others the bones, are more than ordinarily 

 developed, without our being able to assign any other reason for it than 

 that there was a predisposition in the constitution of the individual to 

 such increased nutrition. But generally we can refer the hypertrophy 

 either to excessive exercise of the part, or to the long-continued action 

 of a stimulus upon it. When any part is in a state of activity, a 

 rreater flow of blood takes place towards it than when it is at rest ; and 

 .t is well known that a stimulus such as friction applied to a part of 

 the body causes it to become of a brighter red colour from its vessels 

 treing more injected with blood. If such a state be long kept up, over- 

 nourishment is the result. A popular example of hypertrophy from 

 increased exercise is afforded by the muscles of the arms of the black- 

 smith, or those of the legs of the opera-dancer. The heart also 

 frequently becomes hypertrophied from this cause; for instance, in 

 cases where an increased action of its muscular walls is rendered neces- 

 sary by an obstacle to the passage of the blood, which it propels into 

 the body. Hypertrophy from the second cause, the long-continued 

 operation of a stimulus, is seen hi the thickened state of parts of the 

 skin which have been subjected to friction. But hypertrophy from 

 this cause is seldom simple ; it is generally combined with the depo- 

 sition of new matter of a different nature from the original tissue, the 

 stimulus having excited inflammatory action as well as increased 

 nutrition. 



The treatment of hypertrophy consists in the removal of the exciting 

 cause, if this can be effected : the part should be kept at rest as much 

 as possible, all irritation prevented, and the supply of blood diminished. 

 These means can, however, in very few cases be put into practice to 

 such an extent as to be beneficial, except in arresting the progress of 

 the affection. 



(Andral, Pathological Anatomy ; Carswell, Illustrations of the Ele- 

 mentary Formi of JJiaeate.) 



HYPERURIC ACID (C^N.H.O.), Peruric Acid, discovered by 

 Unger, and formed by acting on guanin with hydrochloric acid and 

 chlorate of potash. It differs in composition from uric acid by 1 equiva- 

 lent of water and 2 of oxygen : hence its name. It is colourless, and 

 crystallises in short rhombic prisms, and when heated is resolved into 

 hydrated cyanic acid, water, and carbon. 



HYPO and HYPER. [CHEMICAL NOMENCLATURE; Nomenclature 

 of Acid*.] 



HYPOCAUSTUM. [BATH.] 

 HYPOCHLORIC ACID. [CHLORINE.] 

 HYPOCHLOROUS ACID. [CHLORINE.] 



HYPOCHONDRIASIS, is a state of extreme sensibility of the 

 nervous system, which leads patients to believe themselves worse 

 than they really are, to detail their sufferings with exaggeration, to 

 individualise all the painful sensations which they experience, and 

 to consider them the symptoms of as many different diseases. Allied 

 to this extreme sensibility there is a mental exaltation, which causes 

 the patients to pay the most minute attention to what passes within 

 themselves. The hypochondriac recounts, without a single omission, 

 all the details of his animal and organic life ; he relates the manner 

 in which his digestion is effected; he numbers the minutes of his 

 sleep ; he describes his sensations, his passions, the succession of his 

 ideas; and dilates on every thing that concerns himself with a 

 copiousness that nothing can arrest. The story which he tells you 

 to-day he will relate again to-morrow, and at ajl times whenever he can 

 find you willing to listen to his tale of sufferings. 



The case of a gentleman is related who was so engaged in attention 

 to himself as to occupy the intervals of the visits of his physician in 

 writing a journal of his sensations. This journal was, at every visit of 

 the physician, produced for his perusal. During a period of several 

 years this gentleman was, without any adequate reason, almost daily 

 in dread of immediate death, and was continually upbraiding his 

 medical attendant and charging him with the greatest cruelty in coming 

 so seldom to see a man in such imminent danger. 



As we do not in general see in hypochondriacs any loss of flesh or 



3 F 



