Page:The New International Encyclopædia 1st ed. v. 17.djvu/75

RESPIRATION. and a ileficicncy of oxygen. The absolute qunn- lity of carbonic acid (and consciiucntly of car- bon) exhaled in 24 hours is liable to j;reat varia- tions, caused by the temperature and moisture of the air, ai,'e, sex, muscular development, the nature and quantity of the food, nuiscular exer- cise, sleep, state of health, etc. Smith calculated that an adult man in a state of rest exhales in 24 hours an amount of carbonic acid equivalent to 7.144 ounces of carbon, and he estimated that it should be increased to 8.GS and 11.7 ounces for non-laliorinj; and laboring persons respectively at their ordinary rate of exertion; that the total amount of carbonic acid is i^rcatly increased by external cold, and diminished tiy heat ; that it is increased by a moist, and diminished by a dry atmosphere; that it increases in both sexes to about the thirtieth year, when it remains station- ary for fifteen years, after which it diminishes ; that at all ages beyond eight years it is greater in males than in females, and that it increases during pregnancy; that it is greater in robust than in slender men, the quantity of carbon ex- pired per diem to each one pomul of bodily weight being (according to Smith) 17.07, 17.51, and 17.99 grains at forty-eight, thirty-nine, and thirty-three years of age respectively; that it is greatly increased by eating, and is diminished by fasting; that it is increased by muscular exertion (>Smith found that when walking three miles an hour he excreted 2.6 more carbonic acid than when at rest, while tread-wheel labor occa- sioned about double the excretion that was caused by walking) ; that it was diminished by sleep; and that it is increased in the exanthematous fevers (measles, smallpox, scarlatina, etc.) and in chlorosis, while it is diminished in typhus and in chronic diseases of the respiratory organs. See MiLscuLAR Force. There has lieen much discussion with regard to the extent to which the nitrogen of the air is affected by respiration. Usually a small amount of this gas is given ofT, but the quantities absorbed and exhaled so nearly balance eacli other that its special action on the organism must be very trifling, fxirthcr than as being a diluter of the oxygen, which would be too stimu- lating if breathed in a pure st;ite. The amount of the watery vapor with which the exhaled air is saturated may range from about to 27 ounces in 24 hours, its usual range being between 7 and 11 ounces. It is not pure water, but holds in solution a considerable amount of carbonic acid and an alliuminous .substance in a state of de- composition, which, on exposing the Huid to an elevated temperature, occasions a very evident putrid odor. See Bronchitis; Pneumonia; Tu- berculosis. The well-known anatomical division.s of the lungs, known as lobes, are composed histolog- ically of an enormous number of little lobes or lobules. Each lobule is separated from sur- rounding lobules by connective tissue, and the lobules which come to the surface of the lung are often distinguishable as little polygonal areas. Each pulmonary lobule consists of a single termi- nal bronchus and the group of air cells and spaces connected with that bronchus. The termi- nal bronchus on entering a lobule divides into several branches knowni as alveolar ducts. These open into considerably laj'ger cavities called in- fundibnla, from the sides of which the air sacs or Vol. XVII.— 6. o9 RESPIRATION. air cells open out lilic alcoves. The terminal bronchus is lined by a single layer of ciliated columnar epithelium. Outside of this are some elastic fibres and thin irregular bundles of smooth nuiscle cells. As the alveolar duels are approached the ciliated epithelium is replaced by lower ei)ithelium of the niin-eiliated variety. In the alveolar ducts the epithelium is eufioidnl, and the elastic tissue and smooth nniscle are greatly reduecil in amount. In the infundibnlum EightBraneltus SinallBfvntttut In/un/f/htii/t/TL 1. Trachea and bronchi. 2. Siiuill tironuhiiHehowiDK air cell anil lobule. 3. Ultiniat* brolii-hus of flog. the epithelium consists mainly of large flat non- nucleated cells known as respiratory ei)ithelium. Among these are scattered smaller polyheilral cells which are remains of foetal life and arc called embryonal cells. Elastic tissue forms the supporting framework of the air sacs and forms a distinct ring around the mouth of each sac. In addition to the clastic tissue there is usually a small amount of fibnms connective tissue and some connective tissue cells surrounding the air sacs. Besides the parts just described, which may be considered as the parenchyma of the lung, there are seen in all sections of lung tissue bronchi of various sizes. The smaller bronchi are lined with a single layer of columnar ciliated epitheliinn lying upon a basement membrane. Beneath the latter is the stroma of the nuieous mendn-anc, outside of which is a circular layer of smooth muscle, the whole being surrounded by a connective tissue or fibrous coat. In the medium size and larger bronchi a distinct sd>- mucous coat is present in which are imlieildcd the acini of nnicous glands, while in the fibrous coat are situated various sized plates of liyalin cartilage. In the largest of the bronchi the epithelium, insti-ad of consisting of a single layer, is made up of several layers, and there is an increase in the thickness of the musculari.s niu- cosie and of the filuous coat. The blood vessels of the lung belong to two distinct systems: one, the bronchial syslein. is for the liourishment of the lung projier; the other, the pulmonary system, is for the purpose of exposing the blood to the air in the lungs. Both systems of vessels enter the lung at the hilus accompanying the large divisions of the bronchus. Within the lung the imlnionary sys- tem of vessels give o(T branches which correspond to the divisions of the bronchi, and on reaching the septa between the infundiliula. break up inl'> an extremely rich network -if capillaries which surround the air sacs. At the margins of the air sacs the blood from the capillary network enters the radicles of the pulmonary veins, which