RESONANCE 



Resonance (Lat. reaonare, to 

 sound back). Production of vibra- 

 tions in a body by the action of a 

 periodic force which has the same 

 period of vibration as the natural 

 period of the body. It occurs fre- 

 quently in sound. If, for example, 

 two tuning forks of the same pitch 

 are held near the other, and one is 

 sounded, the sound waves sent out 

 by it will strike the second fork, and 

 cause the latter to vibrate in 

 unison. 



Resonators are commonly used 

 to increase the amount of the sound 

 of the particular pitch to which 

 they respond, by increasing the 

 amplitude of the sound waves. The 

 sound of a tuning fork may be in- 

 creased by a resonator. The resona- 

 tor employed f^r tills purpose is a 

 pipe closed at one end, open at the 

 other, and the air column of which 

 has a natural period of vibration 

 equal to that of the tuning fork 

 that is, its length is equal to one- 

 fourth of the wave length of the 

 note given by the fork. If now the 

 sounding fork is held near the open 

 end of the pipe, the column of air in 

 the pipe, being a natural resonator 

 to the fork, will be set in vibration. 



If the open end of the pipe is fairly 

 large, the vibrations of the column 

 of air will set the external air in 

 motion more powerfully than th? 

 fork did by itself, and the intensity 

 of the sound will be much increased. 

 The vibration of such columns of 

 air in pipes is made use of in many 

 musical instruments. The sounding 

 hoard of a piano or the body of a 

 violin are also examples of resona- 

 tors, increasing the natural volume 

 of sound. Electric resonance occurs 

 when an electrical circuit has a 

 natural period equal or nearly 

 equal to the period of the source of 

 impulses or alternating electro- 

 motive force. The same kind of 

 effect can be noted in the vibra- 

 tions of a string. See Sound ; Wire- 

 less Telegraphy. 



Resorcin. C 6 H 6 2 . White crys- 

 talline substance obtained by the 

 interaction of fused sodium hy- 

 droxide and sodium metabenzene- 

 disulphonate, or it may be obtained 

 by fusing certain resins with caustic 

 potash, or by distillation of Brazil 

 wood extract. Resorcin appears as 

 colourless crystals soluble in water 

 and alcohol. With the aldehydes it 

 forms formaldehyde. From it are 

 prepared a number of dyes. It ia 

 used in medicine occasionally in cer- 

 tain skin affections, either as a lo- 

 tion or with four parts of glycerine. 



Respiration. Process by which 

 oxygen is conveyed to the blood, 

 and carbon dioxide and water va- 

 pour, the waste products of the tis- 

 sues, are removed. In marine ani- 

 mals this process is effected by 



6573 



means of gills. In land animals the 

 exchange is performed through the 

 lungs. In man the organs through 

 which respiration is effected are 

 the air passages, composed of the 

 larynx, trachea, and bronchi, and 

 the lungs, the structure of each of 

 which is described under its appro- 

 priate heading. The movements of 

 the thorax are caused by certain 

 muscles which, by contracting, 

 bring about an increase in the vol- 

 ume of the chest cavity. The lungs 

 expand with this increase of vol- 

 ume, and air is drawn into them 

 through the air passages. This is 

 the process of inspiration and is a 

 muscular act. The respiratory 

 muscles now relax, and the elastic 

 recoil of the chest and lungs expels 

 the air. This is expiration, and in 

 ordinary quiet breathing entails no 

 muscular effort. 



'inspiration 



Respiration. Diagram illustrating 



the movements of the diaphragm 



during respiration 



The ordinary muscles of respira- 

 tion are : (1) the diaphragm, which 

 is dome-shaped and forms the floor 

 of the thoracic cavity. On con- 

 traction the diaphragm is drawn 

 downwards, and the vertical dia- 

 meter of the chest is increased. 

 (2) The intercostals, or muscles 

 between the ribs. The upper ribs 

 being fixed by the muscles of the 

 neck, the contraction of the inter- 

 costals raises the lower ribs and 

 thus enlarges the lateral and antero- 

 posterior diameters of the thorax. 



In extraordinary or forced in- 

 spiration, such as occurs when 

 there is obstruction to the entry 

 of the air, or in coughing, additional 

 muscles come into play, particu- 

 larly the sterno-mastoid, serratus 

 magnus, pectoral, and trapezius 

 muscles. In forced expiration the 

 abdominal muscles also contract 

 and, by pressing on the viscera, push 

 up the diaphragm and thus help 

 to expel the air from the lungs. 

 In men, the respiratory movements 

 are most marked in the lower part 

 of the chest and the abdomen 

 (inferior costal type). In women, 

 the movements in the upper part 

 of the chest are more marked, and 

 those of the lower part of the 

 chest less obvious (superior costal 

 type). The lungs are not com- 

 pletely emptied at the end of each 

 expiration. 



RESPIRATOR 



The following terms are used for 

 the quantity of air breathed or in 

 the lungs : Tidal air is the amount 

 which is ordinarily breathed in and 

 out, and in a healthy adult man is 

 about 30 cubic ins. Complement*! 

 air is the amount in addition to 

 the tidal air which can be drawn 

 into the lungs by the deepest 

 forced inspiration, and is on the 

 average 100 cubic ins. Reserve or 

 supplemental air is the amount 

 over and above the tidal air which 

 can be expelled by deep forcible 

 expiration, and is about 100 cubic 

 ins. Residual air is the amount 

 which still remains in the lungs 

 after the most violent expiratory 

 efforts, and amounts usually to 

 about 100 cubic ins. 



The effect of continuous muscular 

 effort, as in running a race, is to 

 increase largely the amount of air 

 inhaled and exhaled at each 

 respiration, and the establishment 

 of this process is popularly known 

 as " getting the second wind. " The 

 rate of respiration in a healthy 

 adult is from 14 to 17 per minute. 

 It is increased by exercise, febrile 

 conditions, and certain diseases 

 of the lungs. The total quantity 

 of air inhaled and exhaled during 

 24 hours by a healthy adult varies 

 from 400,000 to 650,000 cubic ins. 

 The regulation of the rhythmic 

 movements of respiration are con- 

 trolled by a respiratory centre in 

 brain, the vagus nerves, and the 

 chemical condition of the blood. 



Cheyne-Stokes respiration is a 

 condition in which the breathing 

 gradually becomes deeper for a 

 brief period, and then shallower 

 until it almost ceases, alternately 

 waxing and waning in a rhythmical 

 manner. It is seen in certain 

 affections of the nerve centres. 



Artificial respiration is the per- 

 formance of certain movements by 

 another person to maintain the 

 respiratory interchange in a person 

 in whom natural breathing has 

 temporarily ceased. It is necessary 

 occasionally in cases of severe 

 shock, as from haemorrhage or 

 surgical operations, poisoning by 

 narcotic substances such as opium, 

 inhalation of non-respirable gases, 

 and drowning. Various methods 

 are employed, the object in each 

 case being to imitate as far as 

 possible the natural movements 

 of the chest in respiration. A 

 description of the process which 

 should be adopted in cases of 

 apparent drowning is given under 

 the heading drowning. See Lung. 

 ' Respirator. Instrument worn 

 over the mouth and nose to protect 

 the wearer from obnoxious par- 

 ticles in the air, from cold, etc. 

 Respirators are often worn by fire- 

 men as a protection against smoke, 



