188 



THE HUMAN MACHINE 



Problem 164: To find out some functions of the skin. 



Materials. Hand lens, ether or alcohol, large glass jar, two 

 thermometers, model or chart of skin. 



Method and Observations. Find out whether all parts of the 

 skin are equally sensitive, by touching with the sharp point of a 

 pencil. Cool a large glass jar, and hold the hand and wrist in 

 the jar for a few moments, closing the opening of the jar with a 

 cloth or a towel. What collects on the inner surface of the jar? 

 What happens when you take violent exercise? Weigh yourself 

 before and after a period of hard work in the gymnasium. Is 

 there any loss in weight? How do you account for it? Place 

 a few drops of ether or alcohol on the back of the hand and note 

 the evaporation of the liquid. What sensation do you feel while 

 the evaporation takes place? 



Study the model or figure, page 342, Civic Biology. Locate the 

 two layers by means of your textbook. Find 

 and describe the sweat glands, oil glands, and 

 sense organs. Draw a diagrammatic sketch of 

 the model and label all parts. Write a state- 

 ment giving the function of each part. 



Conclusion. 1. Is the skin an organ of 

 sensation ? 



2. What passes off through the skin ? 



3. What result to your bodily comfort does 

 this last function have? 



Problem 165: To study the use of the 



muscles. 



Material. Frogs preserved in formalin. 



Method. Remove the skin from the hind 

 leg of a frog. 



Observations. Note the " flesh " forming 

 the muscle of the leg. (The wide part or belly of 

 a muscle is attached to the bone by a tough 

 tendon.) Move the leg by pulling the foot up 

 and down. What effect does this have on the 

 muscle? To what are the muscles attached? 



MUSCLES OF THE 

 LEFT LEG OF THE 

 FROG. 



6, biceps ; g, gastroc- 

 nemius ; sm , 

 semi-membra- 

 nosus ; tr, triceps. 



