iiKMoiiiiiiAdi: 295 



is variably altci't'd aftrr repeated lieiuorrliag'es; the sugar is little 

 affected l>ut the non-jjroteiu nitrogen and urea are increased.'''" Rapid 

 lieniorrhagos cause a decrease in the coagulation time l)ecause of a 

 decrease in antitlirond)in and a sligiit increase in prothrombin, in spite 

 of a decrease in fibrinogen.^-" If the blood is withdrawn repeatedly 

 in large amounts, centrifuged, and the washed corpuscles reinjected 

 suspended in isotonic salt solution (plasmaphaeresis), life can be 

 maintained even after 4 to 5 times the total volume of blood has l)een 

 removed and washed. This is possible because of rapid reformation 

 of the plasma, and the ])lood sliows the changes characteristic of sec- 

 ondary anemias. ^"'^ 



Changes in the Extravasated Blood. — These begin soon after 

 its escape. In most situations sufficient fibrin ferment is formed to 

 cause prompt clotting, but in the pleura and other serous cavities the 

 blood may remain fluid for some time, possibly because of lack of 

 cellular injury that miglit cause liberation of fibrin ferment.-''^ If the 

 blood does not become infected, the rapidity, of subsequent changes 

 depends chiefly upon the location and amount of blood. Small ex- 

 travasations of blood into the tissues are subjected to the action of the 

 tissue cells and of leucocytes emigrating freely from the capillaries; 

 large masses of blood are but little affected by these agencies, the 

 leucocytes within the mass soon die, and secondary changes go on very 

 slowly. In small subcutaneous hemorrhages (e. (/., a bruise) enzymes 

 from the invading leucocytes and tissue-cells soon dissolve the small 

 quantities of fibrin present ; even earlier the stroma of the red cor- 

 puscles is so altered that hemolysis occurs and the hemoglobin escapes 

 and diffuses into the tissues. This hemolysis may be brought about 

 by the action of proteolytic enzjTnes on the corpuscles, or by the hemo- 

 lytic action of the products of protein splitting. Soon the hemoglo- 

 bin disintegrates, forming the masses of pigment so characteristic 

 of old hemorrhagic areas, and also giving rise to the discoloration 

 observed beneath the skin in the later stages of resolution of hemor- 

 rhagic extravasations. The first products of the splitting of hemo- 

 globin are: (1) The protein, glohin, which constitutes 94 per cent, 

 of the hemoglobin; and (2) the iron-containing coloring-matter, hem- 

 atin (in the absence of oxygen the pigment is reduced hematin or 

 hemochromogen). As hematin may be experimentally obtained by 

 the action of proteases upon hemoglobin, the decomposition of the 

 hemoglobin in the tissues is probably accomplished in a similar way 



lOb Taylor and Lewis, Jour. 'Riol. Chom., 19X5 ^22), 71. 



i9i- Drinker, Amer. .Jour. Plivsiol., 1915 '.36). :^0o. 



iMAbel et al. .Tour, rharmacol., Ifll4 (5). (i2.5 ; 101,5 (7), 120. 



20a Denny and Minot (Amor. Jour. Physiol., 1016 (.30). 4-55) believe that the 

 blood really does clot, and that it remains lluid when withdrawn because the 

 fibrinogen has been removed by olottino;. Zahn and Walker (Biochem. Zeit.. 101.3 

 (58). 130). however, consider that the fibrinogen is altered by the pleural endo- 

 thelium, so that it cannot clot. 



