A system of practical medicine. By American authors. Vol. 1

by Unknown

Cohnheim lays special stress upon the presence of micrococci in the softened material, and it is generally agreed that the virulence of septic softening is connected with, if not due to, the presence of microbia. A septic softening may be induced by besmearing, with septic material, the outside of a blood-vessel containing a thrombus, and this form of softening is usually associated with those conditions favoring this relation. Such are the gangrenous wounds following surgical operations, the putrid inflammatory processes affecting the uterine wall after childbirth, the offensive inflammations of the middle ear, and the like. It is possible for a septic softening to occur independently of such contiguous or continuous relations with the surfaces of the body. It is considered, however, that the micrococci present in a softened thrombus must have obtained admission from without through one of the surfaces of the body, mucous or cutaneous, or through undiscovered abrasions of even intact surfaces of peculiar structure, as the alveolar wall or the intestinal mucous membrane. The thrombus is regarded as affording a favorable soil for the growth and activity of the organism.

The mechanical effect of a thrombus varies according to the venous or arterial seat of the same. Venous thrombi, as they are continued toward the heart, tend to become completely obstructing thrombi. In most parts of the body the venous anastomoses are so numerous that the obstruction of a vein is readily compensated for through the collateral venous circulation. When such a compensation is prevented by an extension of the thrombus from branch to branch, and finally to the trunk, an accumulation of blood in the peripheral veins must result. The remote parts become swollen, from the distension of the vessels with blood and the transudation of liquid, and eventually solid material from the blood. Venous thrombosis thus leads to oedema, and even hemorrhage. The more rapidly the obstructing thrombus extends, the earlier and more extreme is the oedema likely to become, while the slower the advance of the thrombus, the more favorable is the opportunity for an enlargement of the collateral vessels through which a sufficient flow of blood is permitted to check oedema and preserve nutrition.

Local mechanical disturbances from arterial thrombi are scarcely perceptible till obstruction is produced, and the results of arterial obstruction will be mentioned in detail in connection with the phenomena of embolism. Cardiac thrombi may occasion local disturbances from interfering with the action of the valves of the heart. Those thrombi which are attached to the valves, especially when calcified, may produce inflammation and aneurism of the opposed wall of the heart, by friction. The most frequent mechanical disturbance from the non-obstructing parietal thrombi of the heart and arteries results from the detachment of fragments and their transfer as emboli to remote parts of the body.

An embolus is a foreign body in a blood-vessel, usually too large to pass through the smallest capillaries, and the disturbances resulting from its presence are included under the term embolism. Although most emboli are detached portions of thrombi, any foreign body of suitable size may become an embolus. Such are tissues, as the pulmonary elastic fibres, fragments of diseased valves of the heart and of the intima of arteries, or portions of tumors growing into vascular canals. Others are globules of oil entering the torn veins when fat-tissue becomes crushed, or air-bubbles admitted through veins either wounded by instruments or opened after parturition by the dislodgment of their obstructing thrombi. Still others are granules of pigment derived from the coloring-matter of the blood, as in melanæmia, or introduced from without, as india-ink and cinnabar. The echinococcus has been found as an embolus, and it is highly probable that the cysticercus, the trichina, and other animal parasites may be disseminated as emboli over the body.

Vegetable parasites, like the bacterium and aspergillus, have also been included in the list, although the disturbances resulting from their presence are less due to mechanical obstruction than to colonization and growth. The experimenter uses the most various objects as emboli—bits of wood, rubber, and glass, globules of mercury, fragments of tissue, etc. Emboli are to be regarded as of arterial or venous origin. The arterial emboli are carried toward the capillaries, while venous emboli are carried toward the heart. The effect of both is partly or wholly mechanical, and partly due to the specific properties of the constituents.

The mechanical effect of an embolus is manifested by the obstruction it offers to the circulation, and the degree of the obstruction depends upon the size, shape, and density of the embolus and the nature and size of the vessel obstructed. An embolus may be so large as to be unable to pass through the valvular orifices of the heart. A long and narrow embolus might pass through a vessel which would not admit one which was short and thick. A jagged and dense embolus, by repeated blows or prolonged and forcible contact, might cause a weakening or rupture of the wall of a vessel, and thus produce an aneurism. Certain vessels (the terminal arteries of Cohnheim) furnish the sole supply of arterial blood to a district, and when they are obstructed, the results, to be mentioned later, differ widely from those taking place where free vascular anastomoses exist. When a trunk bifurcates, the larger branch usually receives the embolus.

Venous emboli are those which approach the heart by the peripheral veins of the body or the pulmonary veins, and the liver by the radicles of the portal vein. Emboli from the veins of the body are carried through the right side of the heart, if not so large as to be stopped at the tricuspid or pulmonary opening. As they enter the latter, they are carried along its course under the influence of gravity and the direction and force of the current, which are determined by the direction and relative size of the bifurcations of the artery, the right primary branch being larger than the left. Eventually, a point of the artery is reached whose diameter is less than that of the embolus, and the latter is stopped. This point usually corresponds with a place of bifurcation, and the embolus frequently rides the wall separating the branches.

Emboli from the radicles of the portal vein owe their most frequent origin to thrombi associated with inflammatory processes in the intestine, especially of the cæcum and vermiform appendage, to inflammatory processes in the spleen and obstruction to the flow of blood through the splenic artery, or to inflammatory changes proceeding from the kidneys. Such venous emboli are carried toward the heart, but are stopped on the way by the intrahepatic branches of the portal vein.

Arterial emboli are those which enter the left side of the heart from the lungs, which arise in the left ventricle or auricle, which may pass through an open foramen ovale from the right auricle, or which arise from the arterial wall. They are carried along the course of the arterial circulation, and are distributed over the different regions and organs of the body. Usually following the more direct course of the circulation, they are more likely to enter the abdominal aorta than to be carried toward the brain or upper extremities. Embolism of the carotids, especially of the left carotid, is more likely to ensue than embolism of the subclavians. Embolism of the coronary arteries is rare, while embolism of the splenic artery, the left renal and left iliac arteries, is comparatively common, and in the order mentioned.

When an embolus is found, or embolism suspected, the source is always to be searched for in those regions from which the affected part receives its blood. The source of arterial and portal emboli is usually found with ease, while the pulmonary embolus may come from so wide a region, the body-veins, that much time may be spent before its place of origin is discovered. An appreciation of the laws of the transfer of emboli renders such a discovery almost certain.