EXCRETION. 143 



2. The tubular sweat glands take the wastes from the lymph which 

 soaks out through the walls of the capillaries in the skin. 



3. The activity of the glands is under control of nerves and nerve 

 centers, as is also the supply of blood to the skin. 



4. The amount of sweat depends on temperature, exercise, amount 

 of liquid food taken, drugs, etc. 



5. The temperature of the body is regulated chiefly by the evapora- 

 tion of sweat. 



6. In cold weather we eat more of ' heat-producing foods, such as 

 fats. 



7. The kidneys excrete urea, a nitrogen-containing waste. 



8. There is an intimate relation between the workings of the lungs, 

 skin, and kidneys. 



Questions. i. Does cutting hair make it grow faster ? 



2. Do cows, dogs, and cats sweat ? 



3. Why is thirst relieved by immersion, even in salt water ? 



4. Why should clothing worn during the day be removed at night ? 



5. How does the body lose heat, except by the skin ? 



6. Why should the blood still be red after passing through the 

 kidney ? 



7. What is "skin grafting" ? 



8. Why is it considered a good sign when the skin becomes moist 

 during a fever ? 



9. Can food, medicine, or poison be absorbed through the skin ? 



