124 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



twenty times its normal work, there is of course a 

 limit to its power, and broken compensation sooner 

 or later follows. 



The vasa vasorum, that carry blood to nourish the 

 walls of both arteries and veins, are very important 

 structures. The coronary vessels of the heart be- 

 long to this class and their course is quite definitely 

 known. Our knowledge of the rest is vague. They 

 ramify through the adventitia and to a less extent 



in the media. If a 



Giant cell. blood - clot forms 



within the vessel, 

 loops from thejvasa 

 vasorum enter the 

 clot and assist in 

 its organization. 



The endothelial 

 cells of the intima, 

 according to one 

 theory, are active 

 agents in preserv- 

 ing the fluid con- 

 dition of the blood ; 

 that is, inhibiting 

 coagulation. If these cells are injured a clot of 

 blood quickly forms upon the injured or denuded 

 surface. Surgeons take advantage of this principle 

 and twist or crush the ends of bleeding vessels to 

 check a hemorrhage. 



The disintegration of red blood-corpuscles is known 

 as hemolysis, and may be produced by injecting into 

 the circulatory system certain poisons, or mixing 

 directly with these poisons. 



Marrow cell. 



Hemaloblast. 



Fat space. 



Fig. 88. Section of red marrow. 



extravasated blood 



