236 



THE BLOOD AND ITS CIRCULATION 



Prohlem "202 : To .^tudy the circulation of the hlood. 



Materials. — Liviiiig tadpole under influence of a 1 per cent 

 solution of chlorotone, mounted on a piece of board having a 

 \ inch hole bored in one end. Place the thin part of the tadpole's 

 tail over the opening ; keep the tadpole moist by wrapping it in 

 wet cotton. (The fin of a living goldfish or the web of a frog's 

 foot may be used.) 



Observations. — Observe the network of small blood vessels 

 containing moving disks, the corpuscles. In some of the tubes the 

 blood appears to move in spurts. These tubes are arteries and 

 lead from the heart. Trace the tiny arteries in the direction the 

 blood flows and notice they divide into very small tubes called 

 capillaries which connect the arteries with tubes called veins. 

 The latter lead back to the heart. How does a capillary differ 

 from a small artery or a small vein ? Does the blood flow in an 

 artery differ from the flow in a vein? Describe the disk-like 

 bodies (red corpuscles) in the blood. How do they compare in 

 size with the diameter of the capillary tube? Make a copy of 

 the following diagram in colors, labeling all parts, showing blue 

 for veins, purple for capillaries, and red for arteries. 



Changes in the Blood within the Capillakies. 



Conclusion. — 1. How does blood get from arteries into the veins ? 



2. What change might take place on the way? Why? 



3. What causes the pulsation (pulse) in the arteries? 



