CHAPTER XVIII 



THE BLOOD 



272. The circulatory system. Nature has provided an 

 intricate arrangement of tubes to conduct food to each cell 

 of the body, and to wash away its waste matter. These 

 two objects are accomplished by the blood. The* conduct- 

 ing tubes and the blood which they contain make the 

 circulatory system. 



273. The blood. About one thirteenth of the body is a 

 red liquid called blood. It consists of a multitude of cir- 

 cular flat red plates, called the red blood corpuscles or cells, 

 floating in a colorless liquid, which also contains a few 



round colorless cells, called white blood 

 corpuscles or cells. 



274. Red blood corpuscles. The red 

 corpuscles of the blood form about 45 per 

 cent of its weight. Each one is a circular 

 flat plate, with rounded edges, and with 

 a depression in the center of each face. 

 Each cell is about -^Vo f an ^ nc ^ * n 

 j- of an inch in thick- 

 ness. Each one is of a reddish yellow 

 color, but when great numbers are piled 

 together they appear bright red. Each corpuscle is com- 

 posed of a jellylike albuminous substance, four fifths of 

 which is a reddish substance called hemoglobin. Hemo- 



156 



Blood corpuscles 

 (x 400). 



a a pile of red blood 

 cells. 



b red blood cells, 



seen flatwise. .. 



c red blood cells, diameter and T 

 seen edgewise. 



d white blood cells. 



