ELEMENTARY PHYSIOLOGY 



found abundantly in stagnant water, called the amoeba. They also, 

 like the amoeba, are constantly shooting out irregular processes, 

 and are therefore said to be capable of amoeboid movements. The 

 colourless corpuscles are not nearly so numerous as the red, the 

 proportion being about one to five hundred. The proportion, 

 however, varies considerably, being dependent on the kind and 

 amount of food taken, age, &c. 



When freshly-drawn blood is allowed to remain at rest for a 

 few minutes it becomes semi-solid and jelly-like by the formation 



of what is called a clot. At first 

 the clot thus formed constitutes 

 the whole mass of the blood, and 

 is of the same uniform colour. 

 But after a short time a very pale 

 yellowish liquid begins to ooze 

 out and collect on the surface. 

 The clot becomes gradually 

 smaller as this liquid exudes, 

 till, at the end of a few hours, 

 it is much firmer, and floats in 

 the yellowish fluid. 



The clot is due to the 

 formation of fibrin a sub- 

 stance which is not present 

 in living blood, but is formed 

 spontaneously, after the blo6d 

 has been drawn, from mate- 

 rials in solution. This change 

 in the blood is termed coagu- 

 lation ; and the liquid which 

 separates from the clot is 

 called serum (whey). The 

 serum is almost entirely free 

 from corpuscles, these being entangled with the fibrin. 



The following tables will assist in making this change clear : 



Fig. in. Blood Corpuscles, as seen 

 under a powerful Microscope. 



", red corpuscles lying flat ; r 1 , red corpuscles 

 on edge and viewed in profile ; r", red cor- 

 puscles arranged in rouleaux ; p and g, colour- 

 less corpuscles. 



Blood (before coagula- 

 tion) 



Liquor sanguinis 



Corpuscles 



Coagulated blood 



I 



'.I 



Water 



Salts 



Albumen 



Fibrin 



Corpuscles 



Water. 



Salts. 



Albumen. 



The elements of fibrin. 



Red. 



Colourless. 



Serum. 

 Clot 



