Page:The New International Encyclopædia 1st ed. v. 17.djvu/76

RESPIRATION. accompany tlic aitciies tn llie surface of the lung. The hioncliial system of vessels accompany the broncliial tubes" anil supply capillary networks to them and to the other structures of the lung. The lymphatics of the lung, like the blood ves- sels, consist of two sets. One of these orij^inates in the lymph spaces of the interlobular con- nective tissue and in the subplcural lymph spaces, communicating by means of the latter with the surface of the pleura. The second set of lymphatics, the bronchial lymphatics, originates in the subepithelial lymiih spaces of the bron- chi, which communicate with the mucous sur- faces of the bronchi and air sacs. From these sjiaees definite lymphatic channels are formed which follow the blood vessels to the surface of the lung and pass thence by means of a few large trunks to the bronchial lymph glands. The nerves of the lung come from both cerebro-spinal and sympathetic systems. Tl'ie main nerve trunks enter the lung at the hilus and follow the branch- ings of the blood vessels and the bronchi. On arriving at the smaller bronchi the nerves break up into fine non-medullated fibrils which pass to the nuiscular tissue and to the mucous mem- brane. RESPIRATION (in plants). A series of processes by which plants release the necessary energy for growtli. movement, and similar work. Although the true nature of respiration was stated by Ingenhouss before the beginning of the nineteenth century and its relation to growth and the evolution of heat was clearly set forth by DeSaussure in 1824, confusion between photosyn- thesis and respiration has persisted to the present day. The method of obtaining energy in the presence of free o.vgen by oxidizing and decomposing materials within the body is known as nor- mal respiration. The process of self-decomposi- tion in the absence of free oxygen is known (in- aptly) as intramolecular respiration; while the process of securing energy by the decomposition of the surrounding medium is designated as fer- mentation. Under ordinary conditions, almost all plants are able to absorb free oxygen from the atmosphere at all times. But if the absorption of free ox.ygen is impossible, the protoplasm may set up such changes in its ow-n substance or in media adjacent to it as to secure the necessary energy by their decomposition. Some of the very simplest plants (anaerobic bacteria) have adapt- ed themselves to this mode of life and flourish only in the absence of free o.xygen. Others (bac- teria, yeasts, molds, etc.) may live and grow in the presence of free oxygen, but when de- prived of this actively decompose the substances with which they are in contact, which are then said to ferment or putrefy. Noriniil respiration consists essentially of four independent processes: flr.st, the absorption of oxygen ; second, the union of oxygen with the sub- stances to be oxidized; third, the decomposition of these substances, with the formation of various end proilvicts, differing according to circum- stances : fourth, the elimination of these products. Its activity varies much with different plants and different parts of the same plant, and is infiu- enccd strikingly by external conditions. Consid- ering only respiration occurring under favorable conditions, that of organs rich in protoplasm is more active than that of watery organs. Thus 60 RESPIRATION. growing points ( buds ) , flowers, seeds, and so on respire more actively than fleshy leaves and tu- bers. The respiration of water and nuvrsh plants is in general less active than that of land plants. The rate of respiration in active plant organs is several times greater per imit of weight than hinuan respiration. The most active respiration recorded is that of young wheat leaves, which consume in 24 hours one gram of o.xygen for each 0.1 gram of their weight. In human respiration one gram of o.xvgen is consiuned per 100 grams of weight. Active aerobic bacteria may consume 200 times as much oxygen as that used by man per unit of weight. 'hen the oxygen pressure is reduced to one-third its normal, respiration is retarded. Under increased pressure the results differ according to the duration of exposure. For a short time plants may respire normally at two to si.x atmospheres of pure oxygen. Under a longer exposure to such pressures respi- ration is likel.v to be retarded. Variations in temperature, which are frequent in nature, exert a double effect; as the temperature rises more oxvgen is absorbed and more CO™ is eliminated. With rising temperature respiration does not, as most functions do, attain a maximum and then diminish with further increase of tempera- ture, but it is accelerated until death ensues. Yet the respiratory rate does not increase in direct proportion to the increase of temperature. Light appears to have little or no effect upon respiration. Intr. MOLECULAR Respiratiox. The exclusion of oxygen from plants which normallv use it pro- duces a profound disturbance of the usual meta- bolism, as shown b.v the fact that the end jirod- ucts of respiration, instead of lieing chiefly carbon dioxide and water, are alcohol, hydrogen, organic acids, etc. For most plants, a period of intra- molecular respiration seems to be a time to be tided over, growth ceases, and most other func- tions are suspended. After the decomposition of the protoplasm has gone to a certain extent, death ensues. Therefore, at high temperatures, which accelerate the process, intramolecular res- piration suflices to maintain life for a shorter time than at low temperatures. See Fermext.- TION. RESPIRATION, Artificial. The exchange of air as in natural breathing (see Respiration, Organs and Process of), produced by mechan- ical means. Respiration is susjjended wiien for any reason the nuiscles concerned in breathing are deprived of their wonted nervous stimulation, by poisoning of the nerve centres which govern them. This may tal;e place in asphyxiation b.v poisonous gases, in drowning, poisoning, or b.v prematurely cutting otT the placental circulation during parturition: and it is in these circum- stances that artificial respiration finds its great- est usefulness. (See Aspiiyxi.v. ) The object in resuscitation (q.v. ) is to imitate as closel.v as possible the natural res]iiratory movements. These should be rh.vthmical and at the rate of twelve or fourteen to the minute. Several methods of carrying on artificial respiration have been devised. Of these the most generally useful is that of S.vlvester. In this method the body of the person to be revived is placed upon the back, the shoulders being slightly elevated, and high enough to keep the chin from falling for- ward on the chest. The arms are then grasped