160 



BLOOD AND LYMPH 



Blood structure. — "We may readily obtain human blood 

 for study at any time by pricking the end of the finger 

 with a clean needle. (See Ex.'XLII.) If we examine a 

 little of the blood so collected on a flat surface we note 

 that the drop is not of the same color thi-oughout. At the 

 edge of the drop it shows a yellowish color while the center 

 is dark red. With the compound microscope we find that 

 this difference in color is due to the fact that blood con- 

 sists of two distinct parts, a yellowish liquid called the 

 plasma, and a vast number of tiny round disks called 

 corpuscles. The red color of the blood is due to the pres- 

 ence of these corpuscles .(red corpuscles). If we use the 

 higher powers of the microscope we find that these red 

 corpuscles are actually biconcave disks (see Fig. 58) 



Fig. 58 — Blood corpuscles ; A^ red corpuscles in rouleaux ; a, a, colorless corpus- 

 cles (X^OO); B, red corpuscles, higlily magnified; C, view of edge; D, three 

 quarters view; JS, red corpuscle swollen with water ; F, Q, IT, distorted red cor- 

 puscles. 



massed together in bands or rouleaux. At the same time, 

 we may be able to make out one or more colorless bodies 

 of irregular shape floating among these bands of disks. 

 These latter are called white corpuscles to distinguish 

 them from the other more numerous form. They differ 

 from the other corpuscles in having a nucleus. Both 

 kinds of corpuscles are cells, but the red corpuscles have 



