8o Physiology. 



color, but a thin layer of the same jelly, as when one takes 

 a spoonful on a plate, has a pale color, more yellowish. 

 The colorless plasma with the colored bodies in it may be 

 compared to a glass dish filled with cranberries and water. 



Hemoglobin. The coloring matter in the blood, then, 

 is wholly in the colored corpuscles. Examination of these 

 corpuscles shows that their color is due to a substance 

 called hemoglobin. The hemoglobin in the corpuscles is 

 the chief agent in picking up the oxygen from the air in 

 the lungs and carrying it to the tissues in the body. 



The Coagulation of Blood. When the blood 'escapes 

 from its natural channels it usually changes from a liquid 

 to a jelly-like condition. This is known as coagulation. 

 It is due to the formation of threads of fibrin from the 

 plasma. These threads of fibrin entangle and inclose the 

 corpuscles, and the two constitute the clot. The liquid 

 that afterward separates from the clot is the serum, and 

 differs from the plasma only in the absence of the fibrin, 

 which is exceedingly*' small in quantity, though of great 

 importance in its action. Coagulation often serves to stop 

 the flow of blood from wounds. 



Fibrin. If freshly drawn blood be stirred rapidly with 

 a little roll of wire screen, there will soon collect on the 

 wires a stringy substance. Thorough washing will soon 

 leave this colorless. It is fibrin. If the stirring has been 

 done thoroughly, the blood will no longer clot, no matter 

 how long it may stand. 



Watching Coagulation. If you have a slight cut on the 

 hand, it will pay to watch the changes in the blood. First 

 it is a red liquid. Then it becomes jelly-like. Then a 

 clear or yellowish liquid comes out ; this is serum. The 

 serum evaporates and the dried clot forms a scab. 



