HYDROSTATIC PRESS 



2890 



HYENA 



where the treatment can be administered. 

 Many state and provincial governments and 

 some local boards of health now provide the 

 Pasteur treatment. The head of the dog 

 should be sent to the nearest laboratory for 

 examination of the brain; this should always 

 be done, for if the active cause of hydropho- 

 bia be not found it will greatly ease the vic- 

 tim's mind, and if it is found the Pasteur 

 treatment can be promptly given. Once con- 

 vulsions set in, the case is hopeless. W.A.E. 



Consult Keirle's Sttidies in Rabies. 



HYDROSTATIC, hi dro stat' ik, PRESS. 

 See HYDRAULIC PRESS. 



HYDROSTATICS, hi dro stat'iks, the term 

 now generally applied to the laws that govern 

 fluids at rest; that is, the laws of liquid and 

 gas pressure. Formerly the study of gas pres- 

 sures was known as pneumatics. 



(1) The primary law of hydrostatics is 

 Pascal's theorem, that fluids transmit pressure 

 equally in all directions. This is easily shown 

 with water, which is far less compressible than 

 a gas. If a bottle whose neck has an opening 

 one square inch in area is filled with water, 

 and a weight of one pound is placed upon the 

 cork, the pressure of the water over each 

 square inch of the inside of the bottle is one 

 pound; or, there is a total pressure of as many 

 pounds as there are square inches on the inner 

 surface of the whole bottle. 



(2) The second law is that the pressure is 

 proportional to the depth and independent of 

 the shape oj the vessel. The more water in 

 the bottle the more pressure will there be 

 on the bottom. The shape, however, is not 

 important, for by the first law pressure is 

 equally distributed. This must be taken into 

 account in the construction of high reservoirs 

 or in harnessing water to drive hydraulic en- 

 gines. 



(3) The third law, known as Archimedes' 

 principle, states that the buoyant jorce on an 

 immersed body is equal to the weight oj the 

 fluid displaced; or, a body is buoyed up by a 

 force equal to the weight of the fluid displaced. 

 It is on this principle that steel ships are built. 

 Steel itself is about eight times heavier than 

 water, but the whole ship displaces a volume 

 of water much greater than the volume of steel 

 in the ship. A balloon will float in the air 

 because it is filled with hydrogen, which is 

 lighter than the same volume of air. 



Gas Pressures. The laws of hydrostatics 

 apply equally to gases, but two others which 



apply to gases only are more directly impor- 

 tant. They are the laws of Charles and Boyle. 

 Boyle's law states that the volume of a given 

 mass of gas at a constant temperature is in- 

 versely proportional to the pressure; that is, 

 as the pressure increases the volume decreases. 

 Charles' law says that if the pressure remains 

 the same, the volume is directly proportional 

 to the temperatures; that is, as the tempera- 

 ture rises, the gas expands. These laws are 

 the basis of all scientific work that involves 

 the motion, elasticity, density, condensation, 

 rarefaction, resistance and weight of gases. 

 See GAS. G.L. 



HYDROSULPHURIC, hi dro sul fu r rik, 

 ACID. See SULPHURETED HYDROGEN. 



HYDROTHERAPY, hi dro ther ' a pi, a word 

 of Greek derivation, meaning literally the 

 treatment of disease with water. As generally 

 understood, the term refers to the systematic 

 use of water at varying temperatures, and with 

 varying methods of application, for the relief 

 of diseased conditions. As an aid to internal 

 surgical treatment it is to be considered of 

 value and has been of service in kidney and 

 liver troubles, nervous disorders of obscure 

 origin, skin troubles and those affecting nutri- 

 tion. The term includes internal as well as 

 external application of water, which, accord- 

 ingly, may be swallowed, used as an injection 

 into vario'is body cavities or applied exter- 

 nally, hot or cold, locally or generally, as the 

 needs of the patient demand. Water treat- 

 ment is ac'ministered at such well-known Euro- 

 pean watering places as Marienbad, Ems, 

 Vichy and Bath, and patients may test the 

 virtues of hydrotherapy in America at Mount 

 Clemens and Battle Creek, Mich., Hot Springs, 

 Ark., Hot Springs, Va., Colorado Springs, 

 Colo., Saratoga Springs, N. Y., and other places 

 of less renown. 



HYENA, hie'na, a skulking, wolflike animal, 

 whose wild howl, sounding like the shrieking 

 laugh of a maniac, fills the night with terror 

 as it prowls about after dark in search of food. 

 The most marked .physical attribute of this 

 animal is its- powerful jaws, which can easily 

 break the bones of an ox, although its main 

 food is the flesh of dead animals. 



The hyena has prominent, ferocious eyes, 

 long, erect ears and very short hind legs which 

 give its body an awkward, hump-backed ap- 

 pearance. There are three species, all of which 

 have long, brown, coarse hair, but are distin- 

 guished by their markings. The most typical 

 and familiar form is the striped hyena, which 



