Specific emboli may be followed by the mechanical effects of simple emboli, but they are also accompanied by specific phenomena which are in relation with the particular focus in which they took origin—i.e. purulent or septic focus, gangrenous cavity, cancerous tumor, etc.
In the region where the embolus is arrested, local alterations of tissue become developed which correspond with the nature of the changes which exist in the spot from which the embolus was derived. Very often these morbid effects are produced without any mechanical results of emboli being occasioned.
Septic emboli are observed in infectious diseases, such as pyæmia and puerperal fever, and are prone to occasion not merely mechanical effects, but equally the suppuration, liquefaction, and finally the absolute destruction of tissue. Cruveilhier has seen pulmonary embolism followed by metastatic abscesses. The formation of these was attributed by him to suppurative phlebitis affecting the capillaries.61
61 Dict. de Méd. et de Chirurgie pratique, vol. xxix. p. 360.
It is admitted to-day that infectious germs causing metastatic abscesses may be transported in the pulmonary vessels without being accompanied by pulmonary emboli. It is equally true, however, that the usual means of transport for these infectious bacteria or micrococci is an embolic plug (Jeannel).
The effects produced by the septic emboli are pneumonic consolidations involving the lobules and going on rapidly to suppuration, and sometimes to gangrene. The coloration of the lobules is red, gray, tending toward yellow as the tissue shows signs of softening. The contents of the abscess are yellow or brown and contain particles of the pulmonary structure. The tissue in the vicinity is gray and infiltrated with pus.
The number of metastatic abscesses is often very considerable. Their size is usually smaller than the infarctus due to simple emboli. The smaller abscesses are found usually near the surface of the lung. When several abscesses unite into one they may attain the size of the fist.
Whenever there exists a gangrenous lesion in some portion of the body, sphacelated débris may be carried from this focus into the venous system, and finally into the lungs. Arrested in some spot of the pulmonary tissue, the embolus will give rise to gangrenous changes similar to those of the region from which it started.62 The infarctus thus produced will assume a dark color, then become gray toward the centre, where it shows signs of softening. Later, under the form of a thick semi-fluid mixture of extreme fetid odor and dark-brownish color, it is expectorated by degrees, and leaves behind a gangrenous cavity. The process of change in this case is due to the proliferation of infectious germs. It may be, however, that the gangrenous particles transported into the lungs have the power in themselves to decompose the tissues by chemical action into more simple elements.63 According to the later researches of Doleris, septic bacteria have been found by him in these putrid infarctions.64
62 This process was first pointed out by Cruveilhier in his work on Phlebitis. It remained, however, for Virchow in his Cellular Pathology (p. 235, ed. Strauss), and later for Billroth in his Surgical Pathology, 1868, p. 395, to give greater development to this belief.
63 Lancereaux, Traité d'Anatomie pathologique, vol. i., 1875–77, p. 14 et seq.