58 Honji) a Co?nplex Afi'wial Uses Food unit iv 



Exercises 



1. How does the feeding of extracts of thyroid gland affect the devel- 

 opment of tadpoles? Place a very m'miite amount of thyroid extract in an 

 aquarium containing tadpoles. Change the water each day before adding^ 

 fresh thyroid extract. Observe and record what changes take place in the 

 tadpoles. What control will you use in this experiment? 



2. Answer the following questions: {a) Because one kind of goiter oc- 

 curs almost entirely in regions where the drinking water lacks iodine, is 

 it reasonable to conclude that this goiter is caused by lack of iodine? 

 Suppose that someone advanced the idea that this type of goiter w as 

 caused by bacteria. How might you find out which hypothesis is cor- 

 rect? {b) Some types of pills which claim to reduce weight have been 

 found to contain relatively large amounts of thyroxin. Would these pills 

 accomplish what they claim to do? Explain. Would it be wise to take 

 such pills without a physician's advice? Explain, (c) Explain why shutting 

 off the blood supply from the thyroid gland would help in the case of an 

 overactive gland. 



3. Do you understand scientific method? The account of the discovery 

 of insulin is more or less typical of all important scientific discoveries. 

 Read the paragraph again carefully. How many centuries did it take 

 before there was much real progress in solving this problem? Why did 

 it take so long? Do you think that the laboratory helper was using any 

 of the methods of science? Explain. Why were the scientists able to make 

 use of this accidental discovery? From what you have just learned, sum 

 up as many of the elements of scientific method as possible. Then list 

 the qualities which a good scientist must possess, and in each case refer 

 to a definite incident. 



4. What truth is there in the statement: "Experimentation speeds up a 

 hundredfold the acquisition of knowledge"? What is there peculiar to 

 an experiment that enables a scientist to get at the truth more quickly? 



5. Study of ductless glands. It is not difficult to obtain specimens of 

 some of the ductless glands from your butcher. Which glands did you 

 obtain? From which part of the animal did they come? What is the size 

 and shape of each? Handle the glands. How does gland tissue differ from 

 muscle tissue? What is the color? Why are large amounts of blood neces- 

 sary to the gland cells? 



Further Actwities in Biology 



1. Look up the story of the discovery of secretin. Report to the class. 



2. Much has been written about the effect of the endocrine glands upon 

 personality. Look up and report to the class on this topic. Be ver\' critical 

 of this work. 



3. Plan other experiments like Exercise i. Consult your teacher before 

 attempting tlicjii. 



