THE COAGULATION OF BLOOD. 



179 



The Colorless Blood Corpuscles are a little larger than 

 the red, but much less numerous (about 1 to 300). As 

 their name implies they contain no coloring matter. Each 

 is a cell with a nucleus, and has the wonderful property of 

 being able to change its own shape. Watched, with a micro- 

 scope the corpuscle may be seen to alter its form slowly 

 (Fig. 55), or even to creep across the glass. These corpus- 

 cles are thus little, independently 

 moving cells which live in our blood. 

 The pus or " matter" which collects 

 in an abscess is chiefly made up of 

 colorless blood - corpuscles which 

 have bored through the walls of 

 the smallest blood-vessels. Their 

 movements are very like those of the 

 microscopic animal named amw'ba, 

 and are accordingly called amoeboid. 



The Coagulation of Blood. When blood is first drawn 

 from the living body it is perfectly liquid, flowing in any 

 direction as readily as water. This condition is only tem- 

 porary; in a few minutes the blood becomes viscid and sticky, 

 and comes to resemble a thick red syrup; the viscidity be- 

 comes more and more marked, until, after the lapse of five 

 or six minutes, the whole mass sets into a jelly which ad- 

 heres to the vessel containing it, so that this may be in- 

 verted without any blood whatever being spilled. This 

 stage is known as that of gelatinization, and is also not per- 



How do the colorless corpuscles differ from the red in size and 

 number? What is each? What property does it possess? What is 

 seen when one is watched with the help of a microscope? What is 

 pus? Why are the movements of the colorless corpuscles called 

 amoeboid? 



What is the consistency of fresh drawn blood? What change 

 occurs in it within a few minutes? 



FIG. 55. A white blood- 

 corpuscle, sketched at suc- 

 cessive intervals of a few 

 seconds to illustrate the 

 changes of form due to its 

 amoeboid movements. 



