82 



BLOOD 



the corpuscular clot it contains fragments of red and white cor- 

 puscles and of fibrin. 



Fibrin. If a specimen of freshly drawn blood be allowed to 

 remain in the field of the microscope, it will be noticed, after 



some time, that fine 

 colorless fibrils appear 

 within the spaces be- 

 tween the corpuscular 

 elements. This forma- 

 tion of fibrin takes 

 place first in the more 

 exposed portions of the 

 specimen at the edge 

 of the cover glass, but 

 in course of time ex- 

 tends throughout the 

 entire specimen. The 

 fine filaments thus 

 formed produce a dense 

 network of interlacing 

 fibrils. This fibrin net 

 eventually contracts, 



FIG. 



J. FIBRILS OF FIBRIN. 



Drawn from the same preparation as is represented 

 in Fig. T4, but only after an interval of several Lours. 

 x 1065. 



drawing with it the 



corpuscles, which are thus crowded into groups to form with the 

 fibrin the denser clot, the fluid serum being expressed into the 

 interval between adjacent masses of clot. 



Careful observation of the earliest formed fibrils of fibrin will 

 show that they can be first recognized about the margins of the 

 groups of blood platelets and in relation to the white blood cor- 

 puscles. This appearance is taken to indicate a close physiolog- 

 ical relation between these elements and the formation of fibrin. 



Hemoglobin. The coloring matter of the blood is a compound 

 of iron with a globulin. This hemoglobin is held either in solu- 

 tion or in loose chemical combination by the cytoplasm of the red 

 blood corpuscles. It escapes from these cells after rupture of 

 their limiting membrane and is then capable of being crystallized 

 in the form of minute brownish-yellow prisms. 



The color of the blood is entirely due to the presence of hemo- 

 globin in its red cells. When examined by transmitted light, so- 

 lutions of hemoglobin and likewise the red blood corpuscles 

 have a faint greenish-yellow or amber color; by reflected light 



