192 THE WONDERFUL HOUSE THAT JACK HAS 



with a pump than to draw it in a bucket? Because 

 when a bucket is used, the top of the well is more or 

 less open, but a tight covering is possible around a 

 pump. It is also a good plan to have the surface 

 surrounding the top of a well slope away from it. 

 Such grading causes the waste water to drain off instead 

 of flowing quickly back into the well and perhaps carry- 

 ing impure substances with it. Melted snow does not 

 make as pure drinking water as a good supply from 

 underground, because the substances taken up during 

 its passage through the air have not been filtered out 

 by the earth. The same thing is usually true of stored 

 rain-water. 



Thus far we have considered the value of water to 

 the inside of the body. Let us now see how it per- 

 forms another very useful service in helping to keep 

 the outside clean and healthy. And what an inter- 

 esting outside covering the skin is ! Its outer or thin 

 layer, called the epidermis, is the part that is raised 

 by a blister, and its chief use is to protect the under 

 layer, called the dermis or true skin. The under side 

 of the epidermis is uneven, and the cells of which it is 

 composed are constantly working up to the surface 

 and being shed. The dermis with the underlying fat 

 serves as a protection to the body. 



The skin contains two sets of tubes called the per- 

 spiratory glands and the oil glands. The perspiratory 

 glands are small tubes lying deep in the true skin or 

 the fat beneath, An outlet, or duct, runs from each 



