136 OUR BODIES AND HOW WE LIVE 



tiny oxygen-carriers are as busy as bees, swirling through 

 the blood vessels. 



The blood has been beautifully called "the river of life." 

 The red corpuscles' may be compared to a countless fleet of 

 little boats which are constantly floating along in this river. 



192. The White Corpuscles. The white corpuscles are 

 slightly larger than the red, and are not flattened. They 

 may sometimes be kept alive under the microscope, and 

 may be seen rolling and tumbling about. At one time 

 they are round like a ball, and of such a size that it would 

 take about twenty-five hundred of them to measure one 

 inch. Shortly afterwards, however, they change this form 

 and become pear shaped, three sided, and so on, in endless 

 variety (Fig. 82). 



The white corpuscles serve as a kind of scavenger for 

 the body. They creep out of "the blood vessels into the 

 tissues and there pick up tiny bits of foreign substances. 

 These corpuscles seem to be warrior cells, forever fighting 

 against the invasion of bacteria. 



Experiment 39. To show the blood corpuscles. Place a small drop 

 of blood (easily obtained by pricking the finger with a needle) upon 

 a clean slip of glass and cover with thin glass, such as is ordinarily 

 used for microscopic purposes. The blood thus spread out into a 

 film may be readily examined with a moderately powerful microscope. 

 At first the red corpuscles will be seen as pale, disklike bodies float- 

 ing in the clear fluid. Soon they will be observed to stick to each 

 other by their concave faces, so as to form rows. Here and there a 

 white corpuscle may be seen among the red ones (Fig. 82). 



193. The Clotting of Blood. If a basin of fresh blood is 

 allowed to stand for a short time, it will separate into two 

 parts : one, a sticky, jellylike mass, called the clot, settles 

 to the bottom; the other, a straw-colored, watery fluid, 



