Circulation, Assimilation and Excretion 421 



auricle of the heart and through the mitral valve back to the left 

 ventricle. The circulation through the lungs is often called the 

 pulmonary circulation, and the circulation through the other parts 

 of the body is called the systemic circulation. Sometimes the 

 circulation through the liver is referred to as the portal circu- 

 lation. 



Experiment to Show Normal Rate of Pulse and a Cause 

 of Variation. The student should take his own pulse while in a 

 quiet state and record the number of beats per minute. Then he 

 should engage in some exercise like running or wrestling. After 

 this the pulse should again be taken and the number of beats per 

 minute recorded as before. The cause of the variation from the 

 first pulse rate will be apparent. 



Experiment to Observe Circulation of Blood in Frog's 

 Foot. Cut a hole in a good sized shingle. Put a frog on the 

 shingle, covering his body with a moist cloth to hold him in posi- 

 tion. Place the web of the foot over the hole in the shingle and 

 hold it in place by tying the toes to pins stuck around the margin of 

 the hole. Then place the webbed part of the foot on the diaphragm 

 of a compound microscope. Look through the lens and observe 

 the movement of blood as it passes through the capillaries of the 

 web membrane. 



The Lymphatics. The lymphatics are a series of pipe-like 

 vessels, sometimes called capillaries, but smaller than the blood 

 capillaries and designed to carry the lymph to the veins. They 

 originate in the spaces between the capillaries and the cells, and 

 gradually unite as they proceed toward the heart, finally form- 

 ing a tube called the thoracic duct, about the size of a goose 

 quill. 



Through this tube the lymph is discharged into the blood. The 

 thoracic duct also receives fatty food in fluid form brought by 

 the lacteals from the small intestine, and transfers it to the blood. 

 The blood passes the waste lymph to the excretory organs, since it 

 is as necessary for waste lymph to be removed as for the waste 

 collected by the veins from the cells to be removed. If waste 

 lymph is not removed, its accumulation in the body will cause 

 the disease known as dropsy. 



