THE SKIN 



27 



Fig. 27. — Plan of a 

 Urinary Tubule, 

 Tb, with artery A, 

 and V in / V. 



Changes in Blood in the Kidneys. — 

 The water holding the nitrogenous 

 waste varies in amount with the 

 amount of water drunk and with the 

 activity of the skin, being less in sum- 

 mer when the perspiration is great. 

 The lungs aid the skin and kidneys 

 in disposing of superfluous moisture. 

 The kidneys have almost the entire 

 responsibility of relieving the body of 

 certain mineral salts and a white crys- 

 talline solid called urea. This is very 

 injurious if retained, causing headaches, rheumatism, and 

 other troubles. 



Thought Questions. Hygiene of the Skin. — 1. What kind of a 

 scar is not affected by freckles or tan? 2. Can a scar on a negro be 

 white? 3. Does a scar on a child grow in size? 4. Why is heat 

 most oppressive in moist weather? 5. How do you account for the 

 shape and location of the usual bald spot? 6. How does the wearing 

 away of the outer cells of the epidermis contribute to the cleanliness of 

 the body? 7. Why does the palm of the hand absorb water more 

 rapidly than the back of the hand? 8. Is it more necessary for mental 

 workers to bathe often or change their clothes often? For physical 

 workers? 9. Is cotton or woolen clothing more liable to stretch or 

 shrink out of shape or size ? To, catch fire? To make the skin clammy 

 with moisture ? To cost more ? To be eaten by moths ? 



