410 LIFE ON THE EARTH 



If this is to be accomplished, the body must be free and 

 not restricted by tight clothing about the chest or the lower 

 part of the trunk of the body, the abdomen. Not only is 

 the right kind of breathing necessary for properly supplying 

 the blood with oxygen, but also that the lung tissues them- 

 selves may be properly nourished and cared for. We 

 should be particularly careful about this now that infec- 

 tious diseases of the lungs are so prevalent. 



Circulation. Experiment 135. If a compound microscope 

 can be procured, tie a string tightly around the end of a clean finger, 

 and when it has become full of blood, prick it quickly with a steri- 

 lized needle. Rub the drop of blood that comes out on a glass 

 slide and quickly examine under the microscope. Notice the great 

 number of round, disklike bodies, red corpuscles. Try to find an 

 irregular-shaped body which, while the blood remains fresh, slowly 

 changes its shape, *a white corpuscle. These are rather difficult 

 to find, but can be seen if the drop of blood is thoroughly examined 

 quickly enough. 



In order that all parts of the body may be provided 



with the materials used in building their cells and in doing 



o c the work necessary for continued 



0< & O Q o$ existence there must be a dis- 



o? o *>o 00 oo o go Q tributory system. Thisisneces- 



^QP oSoO & O T -o i 



30 o o 8 sary wherever diversified work 

 is to be carried on. This neces- 

 sity 'has brought into effect the 

 railway and canal systems of the 

 world. The body is a little world 



FIGURE 132 , ., , -, ., , 



by itself, and it has a most com- 

 plete and wonderfully adapted system for supplying the 

 material needed and for removing the waste. The center 

 and motive power of this system is the heart. The medium 

 of circulation is the blood. 



