HEAT AND CLOTHING 245. 



6. Moisture in the air prevents the evaporation of per- 



spiration, and increases the feeling of warmth. 



7. Fur, silk, woolen, cotton, and linen protect the body 



from cold in the order given. 



8. Raising the temperature of the body causes excite- 



ment and delirium. 



9. Alcohol dilates the arteries of the skin and permits' 



an increased loss of heat, in spite of the feeling of 

 warmth. 



IO. In animals while hibernating, and in all cold-blooded 

 animals, oxidation is feeble, the temperature is low, 

 and their movements are sluggish. 



DEMONSTRATIONS 



97. To show that more blood goes to a part, and that it becomes 

 warmer while acting, let a boy roll up his sleeve and hang his arm by 

 his side. Notice that the veins slowly fill, because the flow of blood is 

 slowed by running up hill. Now have him open and shut his hand 

 rapidly, and notice that at once the veins become filled full of blood. 

 After a moment the hand feels warmer than the other, especially if 

 they were a little cold at first. 



98. Take some ice water, some water at the temperature of the air, 

 and some hot water. Notice that the water at the medium temperature 

 feels warm when the hands have just been taken from the ice water, 

 but cold when they have just been in the hot water. 



99. Feel of a piece of iron and of a stone after exposing both to the 

 cool outside air. Notice that the iron feels colder, for it takes heat 

 from the hand faster. 



100. To show that obstructing the flow of blood makes a part 

 cold, tie a string rather tightly around the finger. In a moment it 

 becomes filled with venous blood, and feels cold, for the blood is 

 not renewed. 



101. That the sensation of heat and cold depends partly upon the 

 amount of blood in the skin can be shown by holding a piece of ice in 

 the hands for several minutes. At first, the hands feel cold, for the 

 arteries are contracted. In a little while the blood circulates freely 



