smell of food, cause dilatation of the vessels of the salivary gland. The mucous membrane of the air passages flush and secrete more actively when a draught of cold air strikes the skin. Ice placed on the abdomen constricts not only the vessels in the skin but those in the kidney. Many other examples might be iven of the control which the vaso-motor system exerts, but the above are sufficient to suggest the influence which the physician can bring to bear on the blood supply of the various organs.
Discussion has taken place as to whether depressor reflexes are brought about by lessening of the vaso-constrictor tone or by excitation of vaso-dilator nerves. Proof of an undoubtable character seems to have been produced that after division of the vaso-constrictor nerves dilatation of a limb can be brought about reflexly by stimulating the depressor nerve, and in this case the effect must be produced by active excitation of the vaso-dilator nerves. Under certain unusual conditions, e.g. deficient supply of oxygen, the vaso-motor centre exhibits rhythmical variations in tonicity which make themselves visible as rhythmical rises and falls of arterial pressure of slow tempo. A waxing and waning of respiration (Cheyne-Stokes breathing) frequently accompanies these waves. Such are observed in sleep, especially in children and in hibernating animals.
Bibliography.—References to all the authoritative papers up to 1892 on the circulation of the blood will be found in Tigerstedt's Lehrbuch der Physiologie des Kreislaufs, and up to 1905-1908 in the articles on the circulation published in Nagel's Handbuch der Physiologie des Menschen, viz. “Allgemeine Physiologie des Herzens, Die innervation der Kreislaufsorgane, ” by F. B. Hofmann, “Die Mechanik der Kreislaufsorgane, " by O. Frank. An elementary introduction to the subject will be found in Leonard Hill's Manual of
Physiology, and a more extensive treatment of it in the same author's article on the “Mechanism of the Circulation," and Gaskell's article on the “Heart” in Schafer's Text-Book of Physiology, or in one of the larger text-books of physiology, such as that of Howell, Stewart Halliburton or Starling.(L. E. H.)
IV. Pathology of the Vascular System
On account of its intimate relations with every part of the body, the circulation is prone to disturbances arising from a great series of causes. Some of these produce effects which may be regarded as functional-mere changes in metabolism, whose disturbances react upon the rest of the body; others give rise to definite structural alterations. In considering the pathology of the circulation, it is useful to divide it into that of the heart, that of the blood vessels and that of the blood.
The heart is liable to changes in the pericardium, malformations, changes in the myocardium, changes in the endocardium valvular lesions and functional disorders.The heart.
(1) The pericardium may become the seat of morbid changes in various cardiac enlargements, it may become stretched or distended; but the most common and im ortant of the changes is an inflammatory one, i.e. pericarditis. This may arise by way of the blood stream, as in rheumatism, scarlatina and other infective diseases, or by way of the lymph stream. The micro-organisms chiefly responsible for the production of pericarditis are the pneumococcus, the different varieties of streptococci and staphylococci, the bacillus tuberculosis, the bacillus coli, and sometimes the gonococcus. In the acute form of the disease the shining serous membrane becomes first dull and lustreless, the blood vessels engorged and an exudation of serum takes place; then fibrin is deposited both on the visceral and parietal layers. When the fluid is insufficient to keep the surfaces apart, the separation at each diastole gives rise to the well-known “friction rub." Sometimes the amount of exudation pent up in the pericardia sac is so great as to necessitate its being drawn off. The fluid may be serous or sero-fibrinous, or may be hemorrhagic, or have undergone a putrefactive change. An effusion of serous fluid into the pericardia sac causes considerable embarrassment to the course of the blood, by rendering the negative pressure, normally present in the sac, positive. The reason for the interference with the circulation brought about by this alteration of pressure is that the auricles are by compression rendered incapable of accommodating the blood-return from the veins. Analogous effects are produced by pressure upon the heart from without, whetheraléy aneurysm or tumour, and pleural effusion or pneumothorax, ecting the viscera from without. In pericarditis it' has further to be remembered that the effect of the process itself upon the muscle Fibres lying beneath the membrane is to cause a softening of texture and weakening of function, whereby the driving power of the heart is diminished. In obliteration of the pericardium, again, the presence of the adhesion's between these two layers leads to interference with the contraction of the myocardium, whereby its functions are interfered with. Acute ventricular dilatation may be associated with pericarditis particularly when the latter is of rheumatic origin and' is the result of the myocardial softening referred- to. Pericardial effusions usually undergo absorption, but various adhesion's, and-thickenings known as “ white spots, ” may remain. Effusions other than inflammatory are found in the pericardium, Le. hydro pericardium, a dropsical accumulation, may be mistaken for an inflammatory one. It occurs in scarlatina, Bright's disease, as part of a general dropsy, or occasionally from some mechanical difficulty interfering with the local circulation. When the fluid is abundant, it may produce the effects noticed under the inflammatory effusion, and the pericardium may become soddened and its endothelium degenerated. Haemopertcardtum, or blood in the pericardium, may occur apart from the amount that may be mixed with inflammatory effusions. It is associated with foreign bodies penetrating from the oesophagus, rupture of an aneurysm, or occasionally associated with scurvy and purpura. Gas and air may sometimes distend the pericardium. It is also liable to new growths, which are usually secondary in character, and tuberculosis and hydatids are sometimes found.
(2) Malformations.—We are ignorant of the causes which lead to imperfect development of the heart. Many of its malformations are of purely pathological interest, but others, such as deficiencies of the intraventricular septum, non-closure of the foramen ovale, patency of the ductus arteriosus, or malformations of the valves, produce a series of secondary effects resultant on the deficient aeration of the blood and sluggishness of the circulation and of venous congestion. The train of symptoms is similar to those mentioned below under acquired valvular lesions, but dropsy is very rare.
(3) The Myocardium.—The coverings of the heart muscle cannot long be diseased without affecting the contractile substance itself. Any morbid changes in the lung tissues which impede the circulation through them, and more particularly emphysema, lead to change in the substance of the right ventricle, while morbid changes in the systemic arteries lead to changes in the left ventricle. In hypertrophy we have an increase of substance. Tangl found by direct measurement that the muscle cells are increased in diameter. The hypertrophy may be due to increased work thrown upon the muscle, as in athletics (idiopathic hypertrophy), or may be compensatory, when the muscle is trying to overcome a circulatory defect, as in valvular stenosis or regurgitation. Hypertrophy, when within physiological limits, is to be considered as a means of adaptation. When occurring in pathological circumstances, it must be regarded as a method, of compensation. Every structure and every function in a healthy body has greater or lesser reserve of energy. In healthy conditions the ordinary demands made upon various organs are far below their possible responses, and if these be excessive in extent or duration, the organs adapt themselves to the conditions imposed on them. In abnormal circumstances the process of hypertrophy is brought about by the power which the structures have .of responding to the demands made upon them; and so long as the process is adequate, all disturbances may be averted. As an example of such readjustment may be cited the fact that in chronic renal cirrhosis, with increased thickness of the middle tunic of the arteries, there is hypertrophy of the left ventricle.
Dilatation of the heart is due to the inability of the heart muscle to expel the contents of its cavities. It may occur from temporary overstress or in the failing 'compensation of valvular disease, or may accompany pathological changes in the muscle such as myocarditis or one of the degeneration's.
From the presence of toxic substances in the blood (whether introduced from without or arising within the body) the cells of the cardiac muscle fibres are apt to undergo what is termed cloudy swelling—the simplest form of degenerative process. The cells become larger and duller, with a granular appearance, and the nuclei are less distinct. As a result of interference with nutrition, whether by simple diminution or perverted processes, fatty degeneration ensues. It may be associated, but is not necessarily connected, with adipose accumulation and encroachment commonly termed infiltration. In true fatty degeneration the muscle cells have part of their protoplasm converted into adipose tissue. The fibres become granular, and the cells lose their definition, while the nuclei are obscure.
The myocardium undergoes both acute and chronic reaction changes. In the former there is enlargement of the nuclei, with proliferation but without karyokinesis. The muscle cells become swollen and lose their striation, while they are softer in texture and altered in outline. The inter muscular tissues are swollen, and may be invaded by leukocytes; this may end in abscess formation or in the .production of newly formed fibrous tissue. Chronic processes affecting the myocardium give rise to a large amount of fibrosis, and the newly formed fibrous tissue separates and compresses the areas of muscle fibres, giving rise to what is commonly known as chronic interstitial myocarditis.
Restitution or recovery may occur to a varying extent in almost all of the disease-processes which have been considered, but it has to be kept in view that in certain of the degenerative affections there is little if any possibility of getting rid of the results of the process, which in the reactive changes terminating in the formation of much fibrous tissue, or its conversion into adipose or calcareous material, the same holds true. Many of the changes, which are
