no doubt in their essence conservative, lead to far-reaching consequences, by their interference with nutritive possibilities.
Diseased conditions of the myocardium are frequently associated with atheromatous degéneratibns of the coronary arteries, and angina pectoris is said to depend upon such state of malnutrition.
The causes which operate by means of the myocardium are almost invariably of a secondary character. The various degenerations already detailed, and the different forms of myocarditis, as well as simple debility of the muscle, are all examples of changes due to general or local disturbance. All processes which directly or indirectly interfere with the energy of the walls of the heart produce twofold effects, by diminishing the aspirator or suction-pump action during diastole, and by lessening its expulsive or Force-pump action during systole. The immediate result upon the heart itself of such disturbances is dilatation of that cavity immediately affected. This may occur under perfectly healthy conditions. In these, however, the dilatation is evanescent, while in the circumstances now under consideration it is permanent, and, although compensated, it leads to persistent dilatation. Upon the blood vessels the result, whether on account of diminished aspirator-y or propulsive energy, is that the amount of blood in the arterial system is decreased, while it, is increased in the venous. It is not a necessary consequence that because there is less blood in the arteries the arterial pressure will be diminished, or the venous pressure increased because the veins contain more than their normal amount of blood, seeing that the blood pressure depends upon many different factors. It is a fact, nevertheless, that in consequence of the alteration in the relative amount of blood in the arteries and veins there is a considerable disturbance of blood pressure. Gravitation may overcome the contractile and elastic factors, and several consequences arise from the resulting venous engorgement. From transudation, oedema of, the dependent parts of the body and the serous membranes occurs. giom the sluggish nature of the current, the blood absorbs too much carbonic acid and loses too much oxygen, hence cyanosis is the result. On account, also, of the slowness of the circulation, there is a longer period for radiation of heat, and the superficial parts of the body accordingly become cold.
The engorgement of internal organs leads to distinct changes in them. The solid viscera, such as the' liver, the spleen, the kidney and the lung, become enlarged and hyperaemic, and if the disturbance be continued, cyanotic atroph ensues. Change in structure, with loss of function, takes place Prom blocking of the vessels by blood-clot, whether due to coagulation on the spot, or by the conveyance thither of clots formed elsewhere; a cirrhotic termination also is not infrequent, although- there is still some doubt whether in this latter condition other:concomitant causes have- not at the same time been operative. The brain, although suffering less from hyperaemia, iS subject to disturbance of the circulation through it, while it is a common seat of embolic and thrombotic processes. The heart itself, lastly, sufférs in consequence of the disturbed circulation through it, and by undergoing venous stasis, with weakening of its walls and increase of its fibrous tissue, it completes the final link in a vicious circle. Effusion into the serous sacs, such as the pleura, the pericardium and the peritoneum, leads to great disturbance of the viscera with which they are connected. The mucous membranes, both respiratory and digestive, become the seat of catarrhal changes in consequence of the backward pressure and impure blood.
(4) Changes in the Endocardium.-In endocarditis, or inflammation of the fining membrane of the heart, that portion of the membrane which covers the valves is invariable-y affected first. Two varieties of endocarditis are' described, simple and infective or ulcerative, but it is difficult to separate them pathologically. Both result from poisoning of the membrane by micro-organisms and their toxins; the mairx- difference seems to lie in the variety of micro-organism present. Simple. endocarditis may be associated with a variety of diseases, acute rheumatism and scarlet fever being the most frequent. In many fatal cases of chorea associated with endocarditis the microtoccus rheuliiaticus has been found in the endocardium, while the streptococci, present in tonsilitié have produced endocarditis in animals. The membrane covering the valves loses its smoothness, granulation's or elevations forming on the free edges; then the endothelium proliferates and is destroyed and fibrin becomes deposited, producing what is termed a “vegetation” In the lower layers of this vegetation microorganisms can be demonstrated. Finally, portions of the vegetation's may be broken off and parried as emboli in the bloodstream, or two valves may become glued together, narrowing the 'opening and producing stenosis, or the deformed valves may be unable to close properly and regurgitation takes place. Thus the lesions of valvular disease are produced. In infective or ulcerative endocarditis, occurring in conjunction with such diseases as pyaemia, septicaemia, smallpox and pneumonia, pyogenic micro cocci are carried into the bood stream, and purulent deposits take place around the valves, In this case, however, the emboli are septic, and when carried to distant tissues produce there ulceration and pus-formation. Numerous abscesses may occur in the wall of the heart muscle itself.
(5) Valvular Lesions.—All the valves of the heart are not equally liable to disease; those most frequently affected are the aortic and mitral valves. We have seen how the lesions, of the valves are brought about., A valvular lesion may actin .two.ways: it may impede the onward flow of the blood by narrowing the orifice, or the mal-closure of the valves -may allowareiiux of blood. Either of these processes may occur at any of the valvular orifices of the heart. Obstruction is usually complicated by some regurgitation as well, though the converse does not hold good. An increase of. the quantity of blood in the auricles, particularly the left, hasa less marked effect on the heart itself than an increase in the contents of the ventricles, owing to the left auricle being in continuity with the pulmonary system: whereas if the amount of blood in the left ventricle be doubled the ventricle must dilate in order to accommodate it. The reserve power of the heart is, called upon to meet the dilatation, the muscular tissues becoming hypertrophied, and a more powerful systole is produced. As the left is the chiet ventricle to undergo this change, the apex of the heart becomes displaced downwards. Similar changes take place in the right ventricle in pulmonary stenosis or tricuspid incompetency. Changes in the right ventricle other than primary valvular disease of the right side of the heart are frequently preceded by mitral incompetence, and are due to extra: pressure being thrown upon the pulmonary semilunar valves by the pressure in the overfull pulmonary system. >In mitral regurgitation the accumulation of blood in the right auricular cavity leads to its dilatation and an engorgement of the pulmonary vessels, pulmonary oedema and induration of the lung, which in turn affects the right heart. Should compensatory hypertrophy of the right ventricle fail to be established, we et the general venous congestion, dropsy and sequence before alluded to.,
(6) Functional Cardiac Disorders.—Cardiac rhythm may be modified in several ways; there may be variation in either the length or the 'strength of the beat, or the beats may not be asynchronous. In palpitation or tachycardia its frequency is increased. This increase depends upon the inhibition of the action of the cardio-inhibitory centre, impulses passing to it from the stomach (as in dyspepsia) or from other organs. Tachycardia is also produced by toxic action, as in diphtheria and Graves's disease. In bradycardia the frequency is diminished. It may be dlié to toxins or to degenerative changes. Intermittence may simulate bradycardia, though the actual rate of the beat is not lessened; but-the weak beats Emil to reach the periphery. Various irregularities may take place, dependent upon perverted nerve action. It is considered that the intrinsic nerve elements play a large part in these; and in some forms of disease the irregularity is of myocardial origin.
The blood vessels possess the properties of Contractility and elasticity in different degrees. Their contractility is characterized by great tonicity; considerable rhythmic action and little or no rapidity of contraction. Their Yessem elasticity stores up energy in a potential condition, and this may be liberated in kinetic form as required. The vessels The blood vessels. are supported in various degrees by the different tissues in which they are found. In the more solid viscera:they are strongly supported, as in the liver and kidney, while in those which are less dense, as in the case of the brain and the lungs, they are not so well sustained.
In many conditions the contractility and elasticity of the blood vessels become diminished according as they may be involved in various pathological processes—purulent, tuberculous or syphilitic. Chronic toxic conditions lead to numerous degenerations, such as fatty degeneration or hyaline degeneration of muscle fibre, apparently as the effect of copulative processes. The tissues assume a somewhat glassy appearance, with a»distinct tendency towards segmentation. Calcareous infiltration is brought about by the deposition of lime salts in tissues which have previously undergone fatty or fibroid changes; It particularly affects the arteries in senile affections. In consequence of maziy toxic agencies as part of a senile change, and as the effect of Ibn -continued stress, the blood vessels undergo a loss of their normal properties. This is compensated by the growth of an excessive amount of fibrous tissue, leading to various forms of arterial sclerosis, of which best known are endafteritis obliteians, which affects the smaller arteries and is due to a toxic irritant and may occur at any age, and endarteritis deformans (atheroma), which affects the larger arteries during middle age, and is usually due to mechanical irritation. As the result of these fibrous changes there is interference with the blood current, since the vessels become unyielding yet frangible, iristead of dis tensile and elastic, tubes. The sclerotic changes lead, moreover, to dilatation of blood vessels, as well as to the formation of definite aneurysms. They also pave the way for cdagulatioxr of blood within them, i.e. thrombosis, while in certain situations, more particularly in the brain and in the kidney, mature is apt to take place. Upon the heart also these changes ring about far-reaching effects. Dilatation, accompanied by hypertrophy, is a certain result of generalized arterial degeneration,
