THE BLOOET, :r -. ^ ^ ; ; /, 101 



THE BLOOD. 



In the examination of the blood it is convenient to 

 consider it as composed of two parts: the corpuscles and 

 the albuminous liquid in which they are suspended, the 

 plasma. The plasma, on standing, separates into two 

 parts by coagulation, the clot or fibrin and a liquid, 

 the serum. 



The reaction of the blood is alkaline from the pres- 

 ence of the carbonate and phosphate of sodium. The 

 specific gravity varies from 1.045 to 1.075, with an aver- 

 age for adult human beings of about 1.055. 



The color of the blood is caused by the red corpus- 

 cles (erythrocytes). Even comparatively thin layers of 

 the blood are opaque from their presence. The coloring 

 matter (ha3inoglobin) can be set free from the corpuscle 

 by water or by many chemical reagents. The color be- 

 comes then much darker, since the light is no longer re- 

 flected from the surface of the corpuscles. This process 

 is called laking. The addition of strong neutral salt solu- 

 tions to blood turns it bright red, because of the increased 

 reflection of light from the shriveled corpuscles. 



The red corpuscles of the same species of animals 

 have the same shape. The average size of those of one 

 animal of a species will be the same as that of any other, 

 although the size of the individual corpuscle may vary 

 greatly in the same animal. In most mammals they are 

 round, biconcave, non-nucleated disks. In the blood of 

 birds, amphibians, and most fishes they are nucleated and 

 more or less elliptical. A single corpuscle when seen un- 

 der the microscope has a yellowish color, not a red. The 

 size of the red corpuscles can be greatly changed by add- 

 ing water or strong solutions of neutral salts. When 



