EMBOLISM 325 



Ziegler, and others had earlier suggested that hyalin thrombi^were formed from 

 red corpuscles. Boxnieyer' independently arrived at the same conclusion as 

 Flexner, in studying hyalin thrombi as the cause of necrosis in the liver of animals 

 infected with the hog-cholera bacillus. Flexner produced hyalin thrombi by 

 injecting corpuscles agglutinated by ricin, or by injecting ricin itself, or hemolytic 

 substances such as ether or foreign serum. As the thrombi become old, the cor- 

 l)uscles lose their form and color and produce the typical hyalin appearance. 

 iVarce'" proved conclusively the dependence of the thrombus formation upon 

 agglutination, for he secured the same results, including the liver necrosis, by 

 injecting specific agglutinating serums. He states that fibrin threads may oc- 

 casionally be found at the periphery of the larger thrombi, but never in the smaller 

 ones. It is extremely probable, from Flexner's observations, that in the thrombosis 

 produced by injecting various toxic substances into the blood, the so-called "fibrin 

 ferment thro7nbosis," the thrombi are merely agglutinative thrombi, devoid of 

 fibrin; this is undoubtedly true for many of the thrombi observed after poisoning 

 with the powerfully agglutinative snake venoms (see Chap. vi). Bacterial hemag- 

 glutinins may also cause the formation of hyalin thrombi.'^ On the other hand, 

 some, at least, of the hyalin capillary thrombi are undoubtedly composed of soft 

 masses of fibrin which have not become fibrillar, although the successful staining 

 by fibrin stain is not final proof of the fibrinous nature of a thrombus. The liver 

 necrosis which follows ether injections in animals is caused by fibrinous thrombi 

 which result from liberation of coagulins by the injured cells (L. Loeb ). 



Secondary Changes in Thrombi. — The changes that occur in thrombi after 

 they have existed for some time are largely due either to ingrowth of new tissue or 

 to calcification, the latter of which will be considered in a separate chapter The 

 only other change of interest from the chemical standpoint is the central softening 

 which may occur in any large thrombus, but is particularly often observed in the 

 large globular thrombi'found in the heart. The center of the thrombus may be 

 so completely softened that it resembles a sac of pus, the contents, according to 

 Welch, consisting of necrotic fatty leucocytes, albuminous and fatty granules, 

 blood-pigment and altered red corpuscles, and occasionally acicular cr^'stals of 

 fatty acids. Undoubtedly this softening is related to the process of fibrinolysis 

 previously described, and depends upon digestion of the fibrin by leucocytic 

 enzymes,^^ but the fact that the central portion alone undergoes softening is of 

 interest, suggesting that the antibodies for leucocytic proteases, which Opie^' 

 found present in normal serum, prevent digestion at the surface of the clot. The 

 same fact indicates that the tissue fibrinolysins^^ do not play an active part in 

 softening clots. 



Embolism 



Emboli offer little of chemical interest, because of the purely me- 

 chanical nature of their origin and of the effects they produce. ^^ An 

 exception exists in the case of fat embolism, for the manner in which 

 the fat is removed from the blood has invited considerable specula- 

 tion.^^ Part of the fat is ehminated in the urine, ^^ but the problem 

 of how it escapes from the glomerular capillaries is not satisfactorily 

 explained; large emboh undoubtedly lead to rupture of the capillary 



9 Jour. Med. Research, 1903 (9), 146. 

 1° Jour. Med. Research, 1904 (12), 329; ibid., 1906 (14), 541. 



11 Pearce and Winne, Amer. Jour. Med. Sci., 1904 (128), 669. 



12 Barker, Jour. Exp. Med., 1908 (19), 343. 



13 Jour. Exper. Med., 1905 (7), 316. 



"Fee Fleisher and Loeb, Jour. Biol. Chem., 1915 (21), 477. 



1* Fat embolism may follow poisoning with potassium chlorate (Winogradow, 

 Virchow's Arch., 1907 (190), 92). 



i« Full discussion by Beneke, Ziegler's Beitr., 1897 (22), 343. 



1' Discussed by Sakaguchi, (Biochem. Zeit., 1913 (48), 1) who finds a little 

 fat in the normal urine. 



