CHANGES IN THE CIRCULATION OF THE BLOOD. 





EMBOLISM. 



Embolism is the stoppage of a blood-vessel by the arrest in its lumen 

 of some material carried along in the circulating blood. The mass caus- 

 ing the stoppage is called an embolus (Fig. 12). This may be composed 

 of a great variety of substances. The most common emboli are detached 

 portions of thrombi, and these may have all the variety 

 of structure which thrombi present. Masses of bac- 

 teria or other parasites, fragments of the heart valves 

 and of tumors, droplets of fat from the medulla of 

 fractured bones (Fig. 13), parenchyma cells, 1 masses 

 of pigment, bubbles of air, etc., may form emboli. 

 Embolism is, in a majority of cases, confined to the 

 arteries and to the branches of the portal vein. 



The primary effect of the stoppage of an arterial 

 trunk is, of course, largely to deprive the region of 

 the body to which its branches are distributed of its 

 normal supply of blood. If the branches of the oc- 

 cluded artery form anastomoses with other arteries 

 beyond the point of stoppage, a collateral circulation 

 may be established and the embolus do no harm. If, 

 however, the occluded vessel be a so-called terminal 

 artery that is, one whose branches do not form an- 

 astomoses with other arteries the result of the em- 

 bolism is quite different. When a terminal artery 

 is occluded by an embolus, the tissue of the affected 

 region usually dies, and there may be an extravasa- 

 tion of blood by diapedesis, leading to the formation of a dark-red, 

 solidified area, called a hcemorrhagic infarction. 2 The area of infarction 

 corresponds to the region supplied with blood by the occluded vessel, 

 and is usually more or less wedge-shaped (Fig. 14). 



After a time the infarction becomes decolorized, inflammatory changes 



1 The presence of liver-cell emboli in the lung capillaries and in the heart clots after 

 traumatic rupture of the liver, and in infectious diseases involving local necroses of the 

 liver has been described by various observers. Emboli believed to be composed largely 

 of placental cells or of cells from the bone marrow are also described under various con- 

 ditions. The facts relating to this subject of parenchyma-cell emboli and its alleged 

 significance may be found summarized by Lubnrsch, Fortschritte der Medizin, Bd. xi., 

 pp. 805 and 845, 1893; and by Aficlioff, Virchow's Archiv, Bd. cxxxiv., p. 11, 1893. 

 Consult also Warthin, The Medical News, September 15th, 1900, Bib!. 



* When an embolus lodges in a terminal artery, and the circulation in the territory 

 supplied by its branches ceases, the pressure from the side of the artery is reduced to 

 zero- but, on the other hand, according to Cohnheim, the venous pressure now makes 

 itself felt in a backward direction, and the capillaries and small veins in the affected 

 region become crowded with blood. This blood is stagnant, however, and the walls of 

 the small vessels, being deprived of their usual nourishment, undergo, it is believed, 

 degenerative changes which favor the occurrence of extensive diapedesis. Thus in the 

 haemorrhagic infarction not only the blood-vessels, but the extravascular tissues also, 

 are crowded with stagnant blood. The researches of Litten make it seem probable that, 

 in most cases, the back pressure in the region of infarction comes, not from the veins, 

 or not from them alone, but from adjacent arterial twigs which communicate with the 

 capillaries of the affected region. 



FIG. 14.- IXFARCTIOXS 

 OF THE SPLEKX. 



