CIRCULATION OF THE BLOOD 395 



causing a disease called f:Y:-":v> ;;:-:: -'; z :-: , Work by Dr. 

 Banting and his co-workers o: Toronto University has resulted 

 in the production of the substance insulin, which contains the 

 hormone. Now :, person whose pancreas has lost the power to 

 regulate the storage of glycogen in the liver may find relief through 

 a proper diet and insulin in prescribed doses. 



Practical Exercise 1. Make a report on some one of the endocrine glands. 



Practical Exercise 2. Statistics show that diabetes is increasing rapidly in 



this country in spite of insulin. The reason given is the rich and heavy diet. 

 What recom m endations would you make for betterment of this condition? 



Self-Testing Exercise 



Hormones are chemical (1) and are produced by 



(2) glands. Underdevelopment of the thyroid causes cretinism, 



overactivity causes (3) (4). The .... (5) 



produce the emergency hormone. The (6) gland seems to 



regulate body size. The pancreas produces a hormone which regu- 

 lates the storage of (7) in the liver. If sugar goes directly 



into the blood, we have (8) and must use (9). 



PROBLEM m. HOW DOES THE BLOOD CIRCULATE 

 THROUGH THE BODY? 



Circulation of the blood. The blood is the carrying agent of 

 the body. Like a railroad system, it takes materials from one 

 part of the human organism to another. Tins it does by means 

 of the organs of circulation, — the heart and blood vessels. These 

 blood vessels are of three kinds: the <:•:-/■;'-/>. elastic muscular 

 tubes, which carry blood away from the heart; the :-;.':<. Thin- 

 walled vessels containing valves which bring the blood back to 

 heart : and the capillaries, which connect the smallest arteries 

 with the smallest veins. The organs of circulation thus form a 

 system of connected tubes through which the blood flows. 



Demonstration 1. What is the structure of the heart ? Refer to the 

 diagram of the heart, with the arteries and veins connected with it. 

 Where do the chief arteries lead to and from where do the large veins 

 come? Obtain the heart of a recently killed steer and examine it. not- 

 ing the four chambers, the valves, and the blood tubes le:\ r : 



