266 EXPERIMENTAL GENERAL SCIENCE 



cut the flow will be steady, but if an artery is injured, the blood 

 will flow in jets corresponding to the heart beats. Arterial 

 blood may also be distinguished from venous blood by being a 

 brighter red. Bleeding from small injuries is usually not long 

 continued. The blood as it reaches the surface tends to 

 thicken and form a clot. This is due to the formation of 

 fibers of a protein called fibrin which entangle the red cor- 

 puscles in their meshes. Slight injuries are best cleansed 

 with water and a mild disinfectant and wrapped with a 

 clean cloth to prevent the entrance of dirt and bacteria. 

 When bleeding is from an artery, the clot may be formed with 

 difficulty, in which case it may be necessary to take up and tie 

 the artery. In order to stop the flow of blood temporarily, 

 the artery may be compressed by a tight bandage between the 

 heart and the point of injury. If the flow is from a large vein, 

 the pressure should be applied on the side of the injury farthest 

 from the heart. 



Practical Exercises 



1. How many places on the body can you find where the pulse may be 

 felt? 



2. Locate the pulse at the base of the thumb on the wrist. How 

 many times does your heart beat a minute? Make three trials. 



3. Count your pulse after running a short distance or climbing one or 

 two flights of stairs. How much has it increased? 



4. After lying down for a few minutes, count your pulse. How does 

 it compare with the count when standing? 



5. Run your finger along the veins on the inside of the forearm, press- 

 ing the blood toward the wrist, and locate the valves in them. 



6. Hold one hand above your head and the other down by your side 

 while you count fifty. Explain the difference noted in the veins on the 

 back of the hand. 



