thorax these same muscles pull down the ribs and sternum. The
M. triangular is sterni, which arises from the back or thoracic
aspect of the sternum and lower costal cartilages and is inserted
into the costal cartilages higher up, can obviously depress the
ribs. So also can the M. serratus posticus inferior, which arises
from the thick fascia of the loins and is inserted into the last
four ribs. So also can the M. quadratus lumborum, which
springs from the pelvis and is attached to the last rib. Indeed
there is hardly a muscle of the body but may be called into play
during extremely laboured respiration, either because it acts on
the chest, or because it serves to steady some part and give a
better purchase for the action of direct respiratory muscles.
Certain Abnormal Forms of Respiration.
Coughing.—There is first a deep inspiration followed by closure of the glottis. Then follows a violent expiratory effort which bursts open the glottis and drives the air out of the lungs in a blast which carries away any light irritating matter it may meet with. The act is commonly involuntary, but may be imitated exactly by a voluntary effort.
Hawking, or Clearing the Throat.—In this act a current of air is driven from the lungs and forced through the narrow space between the root of the tongue and the depressed soft palate. This action can only be caused voluntarily.
Sneezing.—There is first an inspiration which is often unusually rapid; then follows a sudden expiration, and the blast is directed through the nose. The glottis remains open all the time. The act is generally involuntary, but may be more or less successfully imitated by a voluntary effort.
Snoring is caused by unusually steady and prolonged inspirations and expiration's through the open mouth, -the soft palate and uvula being set vibrating by the currents of air.
Crying consists of short deep inspirations and prolonged expiration's with the glottis partially closed. Long-continued crying leads to sobbing, in which sudden spasmodic contractions of the diaphragm cause sudden inspirations and inspiratory sounds generated in larynx and pharynx.
Sighing is a sudden and prolonged inspiration following an unusually long pause after the last expiration.
Laughing is caused by a series of short expiratory blasts which provoke a clear sound from the vocal chords kept tense for the purpose, and at the same time other inarticulate but very characteristic sounds from the vibrating structures of the larynx and pharynx. The face has a characteristic expression. This act is essentially involuntary, and often is beyond control; it can only be imitated very imperfectly.
Yawning is a long deep inspiration followed by a shorter expiration, the mouth, fauces and glottis being kept open in a characteristic fashion. It is involuntary, but may be imitated.
Hiccough is really an inspiration suddenly checked by closure of the glottis; the inspiration is due to a spasmodic contraction of the diaphragm. The closure of the glottis generally leads to a characteristic sound. (A. G.*)
(4) Pathology of the Respiratory System
In the following article we have to give an account of the more important pathological processes which affect the lungs, pleurae and bronchial tubes. In the aetiology of pulmonary affections, the relations between the lungs and the external air, and also between them and the circulatory system, are important. The lungs are, so to speak, placed between the right and left cavities of the heart, and the only way for the blood to pass from the right ventricle to the left side of the heart, except in cases of a patent foramen ovale or other congenital defect forming a communication between the two sides of the organ, is by passing through them. The result is that not only may they become diseased by foreign material carried into them by the blood, but any obstruction to the flow of blood through the left side of the heart tends sooner or later to engorge or congest them, and lead to further changes. Through the nose and mouth they are in direct Connexion with the external atmosphere. Hence the variable condition of the air as regards temperature, degree of moisture, and density, is liable to produce directly various changes in the lungs, or to predispose them to disease; and the contamination of the air with various pathogenic germs and irritating particles in the shape of dust, is a direct source of many lung affections.
Bronchitis, or inflammation of the mucous membrane of the bronchial tubes, has been generally attributed to exposure to atmospheric changes. It occurs with great frequency in the extremes of life, and it is in early childhood and in old age that it is more liable to be fatal. Bronchitis may often follow exposure to cold, but that low temperature in itself is not sufficient to cause it is shown by the fact that the crews of arctic expeditions have been singularly free from diseases usually attributed to cold, but on their return to moist germ-laden atmospheres have at once been affected. Children reared in heated rooms with lack of ventilation are peculiarly susceptible to attacks on the slightest change of temperature. Bronchitis is also frequently caused by cardiac and renal diseases, and by the extension of inflammatory diseases of the upper air passages (as rhinitis, laryngitis or pharyngitis), while blockage of the nasal passages by adenoid or other growths may, by causing persistent mouth-breathing, lead to bronchial infection. Before the bacterial origin of disease was understood, bronchitis was attributed solely to what is termed “catching cold,” and the exact relation of the chill to the bacterial infection is still unknown. It is probable that the chilling of the surface of the body by exposure causes congestion of the mucous membrane, the presence of a virulent micro-organism being then all that is required to produce bronchitis. It is generally accepted that in persons living in the pure air of the country the small bronchi and air-cells are sterile (Barthel in the Zentralblatt für Bakteriologie, vol. xxiv.). Bacteria are arrested on their way by the leukocytes of the nasal mucous membrane and by the vibration of the ciliated epithelium of the upper air passages. The mucous membrane of the upper bronchi is, however, tenanted by various micro-organisms such as the diplo-bacillus of Friedlander, bacillus coli communis, micrococcus tetragenus, &c., and it is considered by William Ewart that these organisms may in certain conditions of their host become virulent. “Specific” bronchitis occurs in the course of a specific infective disease (e.g. influenza, measles or whooping cough) and is due to the specific micro-organism gaining access by the mucous membrane of the respiratory tract. Cases have been known in which the diphtheria bacillus has been so localized. In glanders, small-pox, syphilis and pemphigus, the infective micro-organism is carried to the bronchi by the blood stream. In common or “nonspecific” bronchitis, streptococci, pneumococci and staphylococci are found in the sputum together with Friedlander's bacillus and the bacillus coli communis. Microscopically the bronchi show hyperaemia of the mucous and sub mucous coats, and the whole wall becomes infiltrated with polymorphonuclear leukocytes and round cells- Many cells undergo mucoid degeneration, and there is abundant epithelial proliferation. A large quantity of mucus is secreted by the glands, and the lumen of the bronchi contains an exudate consisting of mucus, degenerated leukocytes and cast-off epithelial cells.
In the rare form of bronchitis known as fibrinous or plastic bronchitis a membranous exudate is formed which forms casts of the bronchi, which may be coughed up. The casts vary from an inch to six or seven inches in length, with branches corresponding to the divisions of the bronchi from which they come. The cast consists of mucus and fibrin in varying proportions. The exact pathology of this variety is still undetermined.
Bronchitis may affect the whole bronchial tract, or more especially the larger or the smaller tubes. It may occur as an acute or as a chronic affection. In the acute form the inflammation may remain limited to the bronchial tubes and gradually subside, or it may lead to inflammation of the surrounding lung tissue, giving rise to disseminated foci of inflammation of greater or less extent throughout the lungs (catarrhal or bronchopneumonia). This is a common complication of bronchitis, especially where the smaller tubes are affected, and is more
