The Blood and its Circulation 



137 



concave in shape. They tend to adhere in long rolls like 

 piles of coins. They are soft, flexible, and elastic, readily 

 squeezing through passages narrower than their own diame- 

 ter, then at once resuming their own shape. 



The principal constituent of these corpuscles, and that 

 which gives them color, is hcemoglobin, a compound con- 

 taining iron and a colorless proteid substance. 

 A very important office of the red corpuscles 

 is to act as carriers of oxygen from the lungs 

 to all of the tissues. 



/ 207. The White Corpuscles. The white cor- 

 puscles are larger than the red, their average 

 diameter being about ^Vfr ^ an mc ^- They 

 are of very irregular shape and stick close to 

 the glass slide on which they are placed. 



The white corpuscles spontaneously undergo 

 active and curious changes of form, resembling 

 those of the amoeba, a very minute organism 

 found in stagnant water (Fig. 2). 



The white corpuscles have been called the 

 warrior-cells of the bodily tissues, forever 

 battling against the invasion of bacteria. 

 They have the power of moving about among 

 the tissues and picking up foreign particles, 

 thus acting as little scavengers. 

 / 208. The Clotting or Coagulation of Blood. 

 When blood is drawn directly from the blood 

 vessels of an animal into a cup it is at first 

 as fluid as water ; but in a few minutes it 

 becomes a jelly-like mass, called a clot. The cup contain- 

 ing it can be, turned upside down, without a drop of blood 

 being spilled. If carefully shaken out, the mass will form 

 a complete mould of the vessel. 



FIG. 66. Hu- 

 man Blood 

 Corpuscles. 



A, red corpus- 

 cles; B, the 

 sa me seen 

 edgeways; C, 

 the same ar- 

 ranged in 

 rows; D , 

 white corpus- 

 cles with nu- 

 clei. 



