22 THE BLOOD. 



THE BLOOD. 

 What is blood? 



Blood, while circulating in the body, is a somewhat viscid, opaque 

 fluid, of a red color ; this color varies in different parts of the body 

 from a brilliant scarlet to a deep purple or nearly black color. It 

 consists of a nearly colorless liquid (plasma or liquor sanguinis), in 

 which swim the blood-corpuscles or globules. 



What are the physical characteristics of blood ? 



It has a specific gravity at 60 F. (15 C.) of 1055 (1045-1062) ; 

 a faintly alkaline (potassium phosphate) reaction ; temperature 

 about 100 F. (37.8 C.) ; a salty taste ; and an odor which is 

 characteristic, and often peculiar to the animal from which it is 

 taken. When taken from the body it tends to form a clot or 

 coagulum (crassamentum). 



What is the quantity of the blood ? 



About one-twelfth of the body-weight, and is distributed as fol- 

 lows in round numbers : 



About one-fourth in heart, lungs, and large vessels ; 



in liver ; 



" in muscles ; 



" in other organs. 



Describe the formation of a clot. 



If blood be drawn into a shallow vessel and exposed to the air, it 

 will become semisolid at the surface in two or three minutes. This 

 jelly-like condition will extend to the sides of the vessel, and then 

 throughout the entire mass, so that if the vessel be inverted the 

 blood will not flow at the end of ten or fifteen minutes. Then 

 drops of pale fluid (serum) begin to appear at the surface, and 

 these unite to form an amount of fluid sufficient in an hour to float 

 the clot, which meanwhile is contracting from the sides of the 

 vessel. The serum continues to exude and the clot to contract for 

 twenty -four to thirty-six hours. The color of the clot remains red, 

 while the serum has a pale straw color. 



Why does blood clot? 



Clotting is due to the formation of a substance called fibrin, 

 which appears as a mesh of fine fibrils and soon entangles the 

 corpuscles. This mesh of fibrin contracts and squeezes out the 



