414. In the human body are found many fluids and solids of dissimilar appearance and character. These are produced by the action of organs, some of which are of simple structure, while others are very complicated in their arrangement. These organs are called Se-cre´to-ry.
415. The SECRETORY ORGANS are the Ex-ha´lants, Fol´li-cles, and the Glands.
416. The EXHALANTS were supposed to be terminations of arteries or capillaries. The external exhalants terminate on the skin and mucous membranes; the internal in the cellular and medullary tissues. (Appendix I.)
Fig. 86.
Fig. 86. A secretory follicle. An artery is seen, which supplies the material for its secretion. Follicles are also supplied with veins and organic nerves.
417. The FOLLICLES are small bags, or sacs, situated in the true skin, and mucous membrane. The pores seen on the skin are the outlets of these bodies.
414. How are the fluids and solids of the body produced? 415–419. Give the anatomy of the secretory organs. 415. Name the secretory organs. 416. Describe the exhalants. What is represented by fig. 86? 417. Define follicles.
418. The GLANDS are soft, fleshy organs, and as various in their structure, as the secretions which it is their function to produce. Each gland is composed of many small lobules united in a compact mass, and each lobule communicates by a small duct with the principal outlet, or duct of the organ. Every gland is supplied with arteries, veins, lymphatics, and nerves. These, with the ducts, are arranged in a peculiar manner, and connected by cellular membrane.
419. There are two classes of glands, one for the modification of the fluids which pass through them, as the mesenteric and lymphatic glands; and the other for the secretion of fluids which are either useful in the animal economy, or require to be rejected from the body.
Fig. 87.
Fig. 87. 1, 1, A secretory gland. 2, 2, Minute ducts that are spread through the glands. These coalesce to form the main duct, 3.
420. Secretion is one of the most obscure and mysterious functions of the animal economy. “It is that process by which various substances are separated from the blood, either with or without experiencing any change during their 194 separation.” Not only is the process by which substances are separated from the blood, called secretion, but the same term is also applied to substances thus separated. Thus physiologists say, that by the process of secretion, bile is formed by the liver; and also, that bile is the secretion of this organ.
418. Give the structure of the glands. 419. How are the glands arranged? 420–431. Give the physiology of the secretory organs. 420. What is secretion?
421. The secreted fluids do not exist in that form in the blood, but most of the elements of which they are made do exist in this fluid, and the “vessels by which it is accomplished may well be called the architects and chemists of the system; for out of the same material—the blood—they construct a variety of wonderful fabrics and chemical compounds. We see the same wonderful power possessed, also, by vegetables; for out of the same materials the olive prepares its oil, the cocoa-nut its milk, the cane its sugar, the poppy its narcotic, the oak its green pulpy leaves, and its dense woody fibre. All are composed of the same few, simple elements, arranged in different order and proportions.”
422. “In like manner we find the vessels, in animated bodies, capable of forming all the various textures and substances which compose the frame; the cellular tissue, the membranes, the ligaments, the cartilages, the bones, the marrow, the muscles with their tendons, the lubricating fluid of the joints, the pulp of the brain, the transparent jelly of the eye; in short, all the textures of the various organs of which the body is composed, consist of similar ultimate elements, and are manufactured from the blood.”
423. Of the agents that produce or direct the different secretions, we have no very accurate knowledge. Some have supposed this function to be mechanical, others a chemical process, but experiments prove that it is dependent on nervous influence. If the nerves are divided which are distributed to 195 any organ, the process of secretion is suspended. It is no uncommon occurrence, that the nature of milk will be so changed from the influence of anger in the mother, as to cause vomiting, colic, and even convulsions, in the infant that swallows it. Unexpected intelligence either of a pleasant or unpleasant character, by its influence on the nervous system, will frequently destroy the appetite. Sometimes mental agitation, as fear, will cause a cold sweat to pervade the surface of the body.
421. What is said respecting secreted substances? Do vegetables possess the property of secretion? 422. From what are the various textures formed? 423. Have we accurate knowledge of the agents that produce secretion?
424. Secretions are constantly maintained, during life, from the serous membrane, by the action of the internal exhalants. The fluid which is exhaled bears some resemblance to the serum of the blood. Its use is to furnish the organs, which are surrounded by this membrane, with a proper degree of moisture, and thus enables them to move easily on each other, as those within the chest and abdomen.
425. The cellular tissue exhales a serous fluid, and when it becomes excessive in quantity, general dropsy is produced. Fat is another secretion, which is thrown out, in a fluid state, from the cellular membrane. It is deposited in little cells, and exists in the greatest abundance between the skin and the muscles. Its use seems to be, to form a cushion around the body for its protection; to furnish nutriment for the system when food cannot be taken; to supply the carbon and hydrogen necessary to sustain the generation of heat, when these articles of combustion are not otherwise furnished. The med´ul-la-ry substance, (marrow,) in the cavities of the long bones, is very much like fat.
Observation. During sickness, if there is not emaciation or absorption of this secretion, it is considered an unfavorable symptom, because it indicates a want of power in the absorbing system, which is among the last to be affected.
How is it proved that secretion depends on nervous influence? 424. What is said of the secretions from the serous membrane? 425. From what tissue is a serous fluid exhaled? What is the effect when this fluid becomes excessive in quantity? What is fat? Its use? What is marrow?
426. The mucous secretion is a transparent, viscid fluid which is secreted by those membranes that line the cavities of the body, which have an external communication, as the trachea and alimentary canal. This secretion serves to protect these parts from the influence of the air, and concurs, by means of its peculiar properties, in the performance of their functions. 427. There are two external secretions, namely, one from the skin, called perspiration, and the other from the lungs. The cutaneous exhalation, or transpiration[14] exists in two forms, called sensible perspiration (sweat) and insensible perspiration. The pulmonary exhalation is the most important and universal, and closely resembles that of the skin.
428. The follicles are found only in the skin and mucous membrane. They secrete an oily, unctuous substance, which mixes with the transpiration, and lubricates the skin. At the root of each hair there is a minute follicle, which secretes the fluid that oils the hair. The wax in the passage of the ear is secreted from these bodies.
429. All the blood distributed to the different glands is similar in composition and character; but the fluids secreted by them, vary in appearance in a remarkable degree. The office of the glands appears to be principally to form different secretions. Thus the salivary glands secrete the insipid saliva; the lachrymal glands, the saline tears; the liver, the yellow, ropy bile; and the kidneys, the acrid urine.
426. What is said relative to the mucous secretion? 427. Name the external secretions. 428. Give the office of the follicles. 429. What appears to be the principal office of the glands? 430. Mention a secretion produced in a particular emergency.
430. Some secretions are evidently produced only in particular 197 emergencies, as is seen in the increased secretion of bony matter when a limb is broken.
431. When any substance which is not demanded for nutrition, or does not give nourishment to the system, is imbibed by the lymphatic vessels, and conveyed into the blood, it is eliminated in the secretions.
Illustration. A few years since, a poor inebriate was carried to a London hospital in a state of intoxication. He lived but a few hours. On examining his brain, nearly half a gill of fluid, strongly impregnated with gin, was found in the cavities of this organ. This was secreted from the vessels of the brain.
432. Unless the secretions are regularly maintained, disease will be the ultimate result. Let the secretions from the skin be suppressed, and fever or some internal inflammation will follow. If the bile is impeded, digestion will be impaired. If any other secretion is suppressed, it will cause a derangement of the various internal organs.
Observation. Ardent spirits derange the secretions, and change the structure of the brain. This is one reason why inebriates do not generally live to advanced age.
433. The quantity of blood influences the character of the secretions. If it is lessened to any great extent, the secretions will be lessened as well as changed in character.
Illustration. When a person has lost a considerable quantity of blood, there is a sensation of thirst in the fauces, attended with a cold, pale, dry skin. When reaction comes 198 on, the perspiration is cold, attended with nausea, and sometimes vomiting.
431. What becomes of those substances imbibed by the lymphatics that do not give nourishment to the body. 432–437. Give the hygiene of the secretory organs. 432. What effect on the system when the secretions are not regularly maintained? 433. Does the quantity of blood influence the secretions? Give an illustration.
434. The secretory organs require the stimulus of pure blood. If this fluid is vitiated, the action of the secretory organs will be more or less modified. Either the quantity will be affected or the quality will be altered.
Observation. The impurity of the blood arising from the inhalation of the vitiated air of sleeping rooms, diminishes and changes the character of the secretions of the mouth and stomach. This accounts for the thirst, coated tongue, and disagreeable taste of the mouth when impure air is breathed during sleep. The disease it induces, is indigestion or dyspepsia.
435. The amount of action modifies the condition of the secretory organs. When a secretory organ is excessively stimulated, its vigor and energy are reduced. The subsequent debility may be so great as to suppress or destroy its functional power.
Illustrations. 1st. In those sections of the country where flax is spun on a “foot-wheel,” it is not unfrequent that the spinners moisten the thread with the secretions of the mouth. This seems to operate economically for a time, but debility of the salivary organs soon follows, which incapacitates them from supplying saliva sufficient to moisten the food, producing in a short time disease of the digestive organs.
2d. The habit of continual spitting, which attends the chewing of tobacco and gums, and other substances, between meals, induces debility, not only of the salivary glands, but of the system generally.
436. One secretory organ may do the office of another. This increased action of a secretory organ may be sustained 199 for a limited time without permanent injury, but, if long continued, a diseased action of the organ will follow. Of morbid secretions we have examples in the ossification of the valves of the heart, cancerous and other tumors.
434. What is the effect of impure blood on the secretory organs? 435. What results from stimulating excessively a secretory organ? How is this illustrated? 436. What is the effect when one secretory organ performs the office of another?
Observation. In the evenings of the warm season, a chill upon the impressible skin, that suppresses the perspiration, is frequently followed by a diarrhœa, dysentery, or cholera morbus. These can be prevented by avoiding the chill. An efficient means of relief, is immediately to restore the skin to its proper action.
437. The secretions are much influenced by the mind. How this is effected, it is difficult to explain; but many facts corroborate it. Every one has felt an increased action of the tear-glands from distressing feelings. Cheerfulness of disposition and serenity of the passions are peculiarly favorable to the proper performance of the secretory function. From this we may learn how important it is to avoid such things as distract, agitate, or harass us.
Observation. In fevers and other diseases, when the skin, mouth, and throat are dry from a suppression of the secretions, let the mind of the patient be changed from despondency to hope, and the skin and the membrane that lines the mouth and throat will exhibit a more moist condition, together with a general improvement of the vital organs of the system. Consequently, all just encouragement of the restoration to health should be given to a sick person.
Give examples of morbid secretions. What is one cause of dysentery and cholera morbus? How can these affections he relieved? 437. Show the influence of the mind on the secretions. Mention instances of its influence.
438. Nutrition is the vital act by which the different parts of the body renew the materials of which they are composed. Digestion, circulation, absorption, and respiration, are but separate links in the chain of nutrition, which would be destroyed by the absence of any one of them.
439. The nutritive process is also a kind of secretion, by which particles of matter are separated from the blood and conveyed with wonderful accuracy to the appropriate textures. The function of the nutrient vessels antagonizes those of absorption: while one system is constructing, with beautiful precision, the animal frame, the other is diligently employed in pulling down this complicated structure.
440. This ever-changing state of the body is shown by giving animals colored matter, mixed with their food, which in a short time tinges their bones with the same color as the matter introduced. Let it be withdrawn, and in a few days the bones will assume their former color—evidently from the effects of absorption. The changeful state of the body is further shown by the losses to which it is subjected; by the necessity of aliment; by the emaciation which follows abstinence from food.
438–454. What remarks respecting nutrition? 438. What is nutrition? 439. What is said of the nutritive process? The function of the nutrient vessels? 440. Give a proof of the ever-changing state of the body. Give other instances illustrative of the changeful state of the body.
441. Every part of the body is subject to this continual change of material, yet it is effected with such regularity, that the size, shape, and appearance, of every organ is preserved; and after an interval of a few years, there may not remain a particle of matter which existed in the system at a former period. Notwithstanding this entire change, the personal identity is never lost.
442. Many calculations have been made to determine in what length of time the whole body is renewed. Some have supposed that it is accomplished in four years; others have fixed the period at seven years; but the time of the change is not definite, as was supposed by a genuine son of the Emerald Isle, who had been in America seven years and three months, and consequently maintained that he was a native American.
Observation. India ink, when introduced into the skin, is not removed; hence some assert that this tissue is an exception to the alternate deposition and removal of its atoms. The ink remains because its particles are too large to be absorbed, and when in the skin it is insoluble.
443. “Those animals which are most complicated in their structure, and are distinguished by the greatest variety of vital manifestations, are subject to the most rapid changes of matter. Such animals require more frequent and more abundant supplies of food; and, in proportion as they are exposed to the greater number of external impressions, will be the rapidity of this change of matter.”
444. “Animals may be situated so that they lose nothing by secretion; consequently, they will require no nutriment. Frogs have been taken from fissures in solid lime rock, which 202 were imbedded many feet below the surface of the earth, and, on being exposed to the air, exhibited signs of life.”
441. Why is the personal identity never lost in the change of materials, which is unceasing in the system? 442. Give the opinion of physiologists respecting the time required for the renewal of the whole body. What exception to the changing state Of the different textures? 443. What animals are subject to the most rapid changes of material? 444. May animals be situated so that they require no nutriment? What is related of frogs?
445. The renovation of the bone, muscle, ligament, tendon, cartilage, fat, nerve, hair, &c., is not perfected merely by the general circulation of the fluid which is expelled from the left side of the heart, but through the agency of a system of minute vessels, which, under ordinary circumstances, cannot be seen by the eye, even when aided by the microscope; still, minute as they are, the function of these agents is necessary to the continuance of life. They are the smallest capillary vessels.
446. “As the blood goes the round of the circulation, the nutrient capillary vessels select and secrete those parts which are similar to the nature of the structure, and the other portions pass on; so that every tissue imbibes and converts to its own use the very principles which it requires for its growth; or, in other words, as the vital current approaches each organ, the particles appropriate to it feel its attractive force,—obey it,—quit the stream,—mingle with the substance of its tissue,—and are changed into its own true and proper nature.”
447. Thus, if a bone is broken, a muscle or a nerve wounded, and, if the system is in a proper state of health, the vital economy immediately sets about healing the rupture. The blood, which flows from the wounded vessels, coagulates in the incision, for the double purpose of stanching the wound, and of forming a matrix for the regeneration of the parts. Very soon, minute vessels shoot out from the living parts into the coagulum of the blood, and immediately commence their operations, and deposit bony matter, where it is required to unite fractured bones, and nervous substance to heal the wounded nerve, &c.
445. Show how the renovation of the bones, muscles, &c., is perfected. 446. What is said of the office of the nutrient capillary vessels? 447. When a bone is fractured, by what process is it healed?
448. But the vital economy seems not to possess the power of reproducing the muscles and true skin, and therefore, when these parts are wounded, the rupture is repaired by a gelatinous substance, which gradually becomes hard, and sometimes assumes something of a fibrous appearance. It so perfectly unites the divided muscle, however, as to restore its functional power. When the cuticle is removed, it is reproduced and no scar remains; but, when the true skin is destroyed, a scar is formed.
449. It is not uncommon that the nutrient arteries have their action so much increased in some parts, as to produce preternatural growth. Sometimes the vessels whose function it is to deposit fat, are increased in action, and wens of no inferior size are formed. Again, there may be a deposition of substances unlike any known to exist in the body. Occasionally, these nutrient arteries of a part take on a new action, and not only deposit their ordinary substance, but others, which they have not heretofore secreted, but which are formed by vessels of other parts of the body. It is in this way that we account for the bony matter deposited in the valves of the heart and brain, also the chalky deposits around the finger-joints.
450. In infancy and childhood, the function of nutrition is very active; a large amount of food is taken, to supply the place of what is lost by the action of the absorbents, and also to contribute to the growth of the body. In middle age, nutrition and absorption are more equal; but in old age, the absorbents are more active than the nutrient vessels. The size, consequently, diminishes, the parts become weaker, the bones more brittle, the body bends forward, and every function exhibits marks of decay and dissolution.
451. A striking instance of active absorption in middle 204 age was exhibited in the person of Calvin Edson, of Vermont, who was exhibited in the large towns of New England, as the “living skeleton.” In early manhood he was athletic, and weighed one hundred and sixty pounds; but the excessive action of the absorbents over the nutrient vessels, reduced his weight, in the interval of eighteen years, to sixty pounds.
448. What occurs when a muscle is divided? 449. State some of the results of an increased action of the nutrient arteries. 450. When is nutrition most active? How in middle age? How in old age? 451. Relate a striking instance of active absorption in middle age.
452. Instances, on the other hand, have occurred, of the action of the nutrient vessels exceeding, in an extreme degree, those of absorption; as in the person of a colored girl, thirteen years of age, who was exhibited in New York in the summer of 1840. She was of the height of misses at that age, but weighed five hundred pounds. Several cases are on record of persons weighing eight hundred pounds.
453. As already mentioned, the blood is the nutritive fluid of animals. When this fluid is coagulated, a thick, jelly-like mass floats in the serum, called coagulum. This coagulated mass is composed of fibrin, and red globulated matter. The color of the red globules is owing to the presence of iron, though some physiologists think it depends on an animal substance of a gelatinous character.
Observation. That portion of the serum which remains fluid after coagulation by heat has taken place, is called se-ros´i-ty. It is more abundant in the blood of old, than in that of young animals; and it forms the “red gravy” in roasted meats.
454. The blood is not necessarily red. It may be white, as in most fish. There is no animal in which the blood is equally red in all parts of the body. The ligaments, tendons, and other white tissues in man are supplied but sparingly with red blood. The fluid that supplies these tissues is whitish.
452. Of excessive nutrition in early life. 453. Describe the parts that enter into the composition of the blood. What part of the blood forms the red gravy in roasted meats? 454. Is the blood necessarily red? Of what color is the blood of the fish? What part of the human system has white blood?
455. Healthy nutrition requires pure blood. If the nutrient arteries of the bones are supplied with impure blood, they will become soft or brittle, their vitality will be impaired, and disease will be the ultimate result. The five hundred muscles receive another portion of the blood. These organs are attached to, and act upon the bones. Upon the health and contractile energy of the muscles depends the ability to labor. Give these organs of motion impure blood, which is an unhealthy stimulus, and they will become enfeebled, the step will lose its elasticity, the movement of the arm will be inefficient, and every muscle will be incapacitated to perform its usual amount of labor.
456. When the stomach, liver, and other organs subservient to the digestion of food, are supplied with impure blood, the digestive process is impaired, causing faintness and loss of appetite, also a deranged state of the intestines, and, in general, all the symptoms of dyspepsia.
457. The delicate structure of the lungs, in which the blood is or should be purified, needs the requisite amount of pure blood to give them vigor and health. When the blood is not of this character, the lungs themselves lose their tone, and, even if permitted to expand freely, have not power fully to change the impure quality of this circulating fluid.
458. The health and beauty of the skin require that the blood should be well purified; but, if the arteries of the skin receive vitiated blood, pimples and blotches appear, and the individual suffers from “humors.” Drinks, made of various 206 kinds of herbs, as well as pills and powders, are taken for this affection. These will never have the desired effect, while the causes of impure blood exist.
455–462. Give the hygiene of nutrition. 455. What is the effect of impure blood upon the bones? On the muscles? 456. On the digestive organs? 457. On the lungs? 458. What is the effect if the vessels of the skin are supplied with vitiated blood?
459. If the nutrient arteries convey impure material to the brain, the nervous and bilious headache, confusion of ideas, loss of memory, impaired intellect, dimness of vision, and dulness of hearing, will be experienced; and in process of time, the brain becomes disorganized, and the brittle thread of life is broken.
Observations. 1st. An exertion of any organ beyond its powers, induces weakness that will disturb the nutrition of the part that is called into action; and it recovers its energy more slowly in proportion to the excess of the exertion. The function of the organ may be totally and permanently destroyed, if the exertion is extremely violent. We sometimes see palsy produced in a muscle simply by the effort to raise too great a weight. The sight is impaired, and total blindness may be produced, by exposure to light too strong or too constant. The mind may be deranged, or idiocy may follow the excess of study or the over-tasking of the brain.
2d. When the function of an organ is permanently impaired or destroyed by over-exertion, the nutrition of the part is rendered insufficient, or is entirely arrested; and then the absorbents remove it wholly or partially, as they do every thing that is no longer useful. Thus, in palsied patients, a few years after the attack, we often find scarce any trace of the palsied muscles remaining; they are reduced almost to simple cellular tissue. The condition of the calf of the leg, in a person having a club-foot, is a familiar proof of this.
460. The blood may be made impure, by the chyle being deficient in quantity or defective in quality. This state of 207 the chyle may be produced by the food being improper in quantity or quality, or by its being taken in an improper manner, at an improper time, and when the system is not prepared for it. The remedy for impure blood produced in any of these ways is to correct the injudicious method of using food. (See Chapters XV. and XVI.)
459. How does impure blood affect the brain? What is the effect when any organ is exerted beyond its powers? What is the effect when an organ is permanently impaired? 460. How may the blood become impure?
461. The blood may also be rendered impure, by not supplying it with oxygen in the lungs, and by the carbon not being eliminated from the system through this channel. The remedy for “impurities of the blood,” produced in this manner, would be, to carefully reduce to practice the directions in the chapters on the hygiene of the respiratory organs, relative to the free movements of the ribs and diaphragm, and the proper ventilation of rooms.
462. A retention of the waste products of the skin produces impure blood. When the vessels of the skin, by which the waste, useless material is eliminated from the system, have become inactive by improper and inadequate clothing, or by a want of cleanliness, the dead, injurious atoms of matter are retained in the circulatory vessels. The only successful method of purifying the blood and restoring health when this condition exists, is to observe the directions given relative to clothing and bathing. (See Chapters XXXIII. and XXXIV.)
Observation. If the blood has become “impure,” or “loaded with humors,” (an idea generally prevalent,) it is not and cannot be “purified” by taking patent pills, powders, drops, &c. But, on the contrary, by observing the suggestions in the preceding paragraphs, the blood can be freed of its impurities, and, what is of greater importance, such “injurious humors” will be prevented.
461. Mention another means by which the blood may be made impure. How remedied? 462. What is the effect of want of cleanliness upon the blood? What is said respecting “humors” in the blood?
Fig. 88.
Fig. 88. A front view of the organs within the chest and abdomen. 1, 1, 1, 1, The muscles of the chest. 2, 2, 2, 2, The ribs. 3, 3, 3, The upper, middle, and lower lobes of the right lung. 4, 4, The lobes of the left lung. 5, The right ventricle of the heart. 6, The left ventricle. 7, The right auricle of the heart. 8, The left auricle. 9, The pulmonary artery. 10, The aorta. 11, The vena cava descendens. 12, The trachea. 13, The œsophagus. 14, 14, 14, 14, The pleura. 15, 15, 15, The diaphragm. 16, 16, The right and left lobe of the liver. 17, The gall-cyst. 18, The stomach. 26, The spleen. 19, 19, The duodenum. 20, The ascending colon. 21, The transverse colon. 25, The descending colon. 22, 22, 22, 22, The small intestine. 23, 23, The abdominal walls turned down. 24, The thoracic duct, opening into the left subclavian vein, (27.)
463. The nutrient portion of the food is poured into the left subclavian vein, (24, 27, fig. 88,) at the lower part of the neck, and is carried to the right cavities of the heart. The fluid in these cavities consists of the chyle incorporated with the impure blood. Neither of these two elements is fitted to promote the growth or repair the waste of the body. They must be subjected to a process, by which the first can be converted into blood, and the second freed of its carbonic acid gas and water. This is effected by the Respiratory Organs.
464. The RESPIRATORY ORGANS are the Lungs, (lights,) the Tra´che-a, (windpipe,) the Bronch´i-a, (subdivisions of the trachea,) and the Air-Ves´i-cles, (air-cells at the extremities of the bronchia.) The Di´a-phragm, (midriff,) Ribs, and several Muscles, also aid in the respiratory process.
465. The LUNGS are conical organs, one on each side of the chest, embracing the heart, (fig. 88,) and separated from each other by a membranous partition. The color of the lungs is a pinkish gray, mottled, and variously marked with black. Each lung is divided into lobes, by a long and deep 210 fissure, which extends from the posterior surface of the upper part of the organ, downward and forward, nearly to the anterior angle of the base. In the right lung, the upper lobe is subdivided by a second fissure. This lung is larger and shorter than the left. It has three lobes, while the left has only two.
463. What fluids are conveyed into the right cavities of the heart? What is necessary before they can be adapted to the wants of the body? By what organs are these changes effected? 464–474. Give the anatomy of the respiratory organs. 464. Name the respiratory organs. What organs also aid in the respiratory process? 465. Describe the lungs.
Fig. 89.
Fig. 89. A back view of the heart and lungs. The posterior walls of the chest are removed. 1, 2, 3, The upper, middle, and lower lobes of the right lung. 8, 9, 10, The two lobes of the left lung. 6, 13, The diaphragm. 7, 7, 14, 14, The pleura that lines the ribs. 4, 11, The pleura that lines the mediastine. 5, 12, 12, The portion of the pleura that covers the diaphragm. 15, The trachea, 16, The larynx. 19, 19, The right and left bronchia. 20, The heart. 29, The lower part of the spinal column.
Explain fig. 89.
466. Each lung is enclosed, and its structure maintained by a serous membrane, called the pleu´ra, which invests it as far as the root, and is thence reflected upon the walls of the chest. The lungs, however, are on the outside of the pleura, in the same way as the head is on the outside of a cap doubled upon itself. The reflected pleuræ in the middle of the thorax form a partition, which divides the chest into two cavities. This partition is called the me-di-as-ti´num.
Fig. 90.
Fig. 90. The heart and lungs removed from the chest, and the lungs freed from all other attachments. 1, The right auricle of the heart. 2, The superior vena cava. 3, The inferior vena cava. 4, The right ventricle. 5, The pulmonary artery issuing from it. a, a, The pulmonary artery, (right and left,) entering the lungs. b, b, Bronchia, or air-tubes, entering the lungs. v, v, Pulmonary veins, issuing from the lungs. 6, The left auricle. 7, The left ventricle. 8, The aorta. 9, The upper lobe of the left lung. 10, Its lower lobe. 11, The upper lobe of the right lung. 12, The middle lobe. 13, The lower lobe.
Observation. When this membrane that covers the lungs, 212 and also lines the chest, is inflamed, the disease is called “pleurisy.”
466. By what are the lungs enclosed? What is the relative position of the lungs and pleura? What is said of the reflected pleuræ? Explain fig. 90. What part of the lungs is affected in pleurisy?
467. The lungs are composed of the ramifications of the bronchial tubes, which terminate in the bronchial cells, (air-cells,) lymphatics, and the divisions of the pulmonary artery and veins. All of these are connected by cellular tissue, which constitutes the pa-ren´chy-ma. Each lung is retained in its place by its root, which is formed by the pulmonary arteries, pulmonary veins, and bronchial tubes, together with the bronchial vessels and pulmonary nerves.
468. The TRACHEA extends from the larynx, of which it is a continuation, to the third dorsal vertebra, where it divides into two parts, called bronchia. It lies anterior to the spinal column, from which it is separated by the œsophagus.
469. The BRONCHIA proceed from the bifurcation, or division of the trachea, to their corresponding lungs. Upon entering the lungs, they divide into two branches, and each branch divides and subdivides, and ultimately terminates in small sacs, or cells, of various sizes, from the twentieth to the hundredth of an inch in diameter. So numerous are these bronchial or air-cells, that the aggregate extent of their lining membrane in man has been computed to exceed a surface of 20,000 square inches, and Munro states that it is thirty times the surface of the human body.
Illustration. The trachea may be compared to the trunk of a tree; the bronchia, to two large branches; the subdivisions of the bronchia, to the branchlets and twigs; the air-cells, to the buds seen on the twigs in the spring.
470. The AIR-VESICLES and small bronchial tubes compose 213 the largest portions of the lungs. These, when once inflated, contain air, under all circumstances, which renders their specific gravity much less than water; hence the vulgar term, lights, for these organs. The trachea and bronchial tubes are lined by mucous membrane. The structure of this membrane is such, that it will bear the presence of pure air without detriment, but not of other substances.
467. Of what are the lungs composed? How retained in place? 468. Where is the trachea situated? 469. Describe the bronchia. What is the aggregate extent of the lining membrane of the air-cells? To what may the trachea and its branches be compared? 470. What is said of the air-cells and bronchial tubes?
Fig. 91.
Fig. 91. A representation of the larynx, trachea, bronchia, and air-cells. 1, 1, 1, An outline of the right lung. 2, 2, 2, An outline of the left lung. 3, The larynx 4, The trachea. 5, The right bronchial tube. 6, The left bronchial tube. 7, 7, 7, 8, 8, 8, The subdivisions of the right and left bronchial tubes. 9, 9, 9, 9, 9, 9, Air-cells.
What membrane lines the trachea and its branches? What is peculiar in its structure? What does fig. 91 represent?
Observation. The structure of the trachea and lungs may be illustrated, by taking these parts of a calf or sheep and inflating the air-vesicles by forcing air into the windpipe with a pipe or quill. The internal structure may then be seen by opening the different parts.
471. The lungs, like other portions of the system, are supplied with nutrient arteries and nerves. The nervous filaments that are distributed to these organs are in part from the tenth pair, (par vagum,) that originates in the brain, and in part from the sympathetic nerve. The muscles that elevate the ribs and the diaphragm receive nervous fibres from a separate system, which is called the respiratory.
Fig. 92.
Fig. 92. 1, A bronchial tube. 2, 2, 2, Air-vesicles. Both the tube and vesicles are much magnified. 3, A bronchial tube and vesicles laid open.
Observation. When the mucous membrane of a few of the larger branches of the windpipe is slightly inflamed, it is called a “cold;” when the inflammation is greater, and extends to the lesser air-tubes, it is called bronch-i´tis. When the air-cells and parenchyma become inflamed, it is called inflammation of the lungs. Coughing is a violent expulsory effort by which air is suddenly forced through the bronchia and trachea to remove offending matter.
How may the structure of the trachea and its branches be illustrated? 471. Are the lungs supplied with nutrient arteries? Where are the respiratory nerves distributed? From what source do these organs derive their nervous filaments?
472. The RIBS are joined to the spinal column at their posterior extremity; and in front, they terminate in cartilages, which unite them to the sternum. They incline downward, from the spinal column to the breast-bone, and form resisting walls that assist in producing the partial vacuum necessary for inspiration.
Fig. 93. A section of the chest when the lungs are inflated. 1, The diaphragm. 2, The muscular walls of the abdomen.
Fig. 94. A section of the chest when the lungs are contracted. 1, The diaphragm in common expiration. 2, 2, The muscular walls of the abdomen. 3, The position of the diaphragm in forced expiration.
These engravings show the diaphragm to be more convex, and the walls of the abdomen more flattened, when the lungs are collapsed, than when they are inflated.
473. The DIAPHRAGM is a flexible circular partition, that separates the respiratory from the digestive organs, and the chest from the abdomen. Its margin is attached to the spinal column, the sternum, and cartilages of the lower ribs. The lungs rest upon its upper surface, while the liver and stomach 216 are placed below it, (fig. 88.) In a state of repose, its upper surface forms an arch, the convexity of which is toward the chest. In forced expiration, its upper point reaches as high as the fourth rib. In an ordinary inspiration, it is depressed as low as the seventh rib, which increases the capacity of the chest.
472. Describe the ribs. Explain figs. 93 and 94. 473. Describe the diaphragm.
474. The RESPIRATORY muscles are, in general, attached at one extremity to the parts about the shoulders, head, and upper portion of the spinal column. From these, they run downward and forward, and are attached, at the opposite extremity, to the sternum, clavicle, and upper rib. Other muscles are attached at one extremity to a rib above, and by the opposite extremity to a rib below. These fill the spaces between the ribs, and, from their situation, are called in-ter-cost´al muscles.
Observation. 1st. There are several actions of common occurrence, that are intimately connected with respiration; such as hiccough, sneezing, &c. Hiccough is an involuntary contraction of the muscles of respiration, particularly the diaphragm.
2d. Sneezing is a violent, involuntary contraction of the respiratory muscles, as in hiccough. When an acrid stimulant, as snuff, is applied to the mucous membrane of the nose, an irritation is produced which is accompanied by a violent expulsion of air from the lungs. This is owing to the connection between the nasal and respiratory nerves.
What is its form when not in action? 474. Where do the respiratory muscles make their attachment? What name is given to those muscles that fill the places between the ribs? What is hiccough? What is sneezing?