272 DISTURBANCES OF CIRCULATION 



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 uecrotic fatty leucocytes, 

 albuminous and fatty granules, blood-pigment and altered red 

 corpuscles, and occasionally acicular crystals of fatty acids. 

 Undoubtedly this softening is related to the process of fibrinol- 

 ysis previously described, and depends upon digestion of the 

 fibrin by leucocytic enzymes ; but the fact that the central por- 

 tion alone undergoes softening is of interest, suggesting that the 

 antibodies for leucocytic proteoses, which Opie 1 found present 

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



EMBOLISM 



Emboli offer little of chemical interest, because of the purely 

 mechanical 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 con- 

 siderable speculation. 2 Part of the fat is eliminated in the 

 urine, but the problem of how it escapes from the glomerular 

 capillaries is not satisfactorily explained ; large emboli undoubt- 

 edly lead to rupture of the capillary walls, and probably some 

 fat also escapes through stomata or similar intercellular open- 

 ings. Fat may also escape in the bile, and some is probably 

 taken up by the tissue and endothelial cells by phagocytosis. 

 Beneke found that the fat becomes partly emulsified by the 

 mechanical action of the blood current, aided to a slight extent 

 by saponification. The larger droplets after lodging in the 

 capillaries are surrounded by leucocytes, to which Beneke 

 ascribes an active part in the removal of the fat as fine droplets 

 by phagocytic action. We may well believe, however, that the 

 lipase of the plasma is an important agent in disintegrating the 

 emboli, although its action is limited because of the relatively 

 small surface which the large drops offer for attack. After fat 

 droplets have been taken into the cells, they presumbly are 

 utilized in metabolism like normally acquired fat, as described 

 previously. 



Air embolism presents some features of interest from the 

 chemical standpoint, especially in those cases following sudden 

 decrease in atmospheric pressure in persons who have been 

 exposed for some time to pressures considerably higher than 



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



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



