134 



THE INTERNAL ENVIRONMENT OF THE BODY 



Part III 



Fig. 8.7. Masai giraffe. Although giraffes belong to the deer family they never 

 shed their stubby antlers which are knobs of bone permanently in the velvet. 

 (Courtesy, New York Zoological Society.) 



e.g., soles of the feet, pads, hoofs (man, elephant, horse), by scales (fishes, 

 reptiles, feet of birds), by feathers and hair, by secretions (mucus in fishes, 

 frogs and toads, mild poisons of hydras, caterpillars of gypsy moths). 



The skin is a receptor of stimuli through sensory cells and nerve endings, 

 sensitive to touch, heat, cold, and pain. 



Skin takes part in the heat regulation of the body: in mammals through 

 control of surface blood vessels, through evaporation of sweat from the body 

 surface (man, horse), by coverings of the body, i.e., by hair, or feathers. 



Vitamin D is produced through irradiation or the exposure to sunshine of 

 oils in skin and on feathers and hairs. In licking their fur mammals secure 

 irradiated oil containing vitamin D involved in the metabolism of calcium and 

 phosphorus. 



Sweat glands located in the skin excrete products of metabolism, such as 

 water, small amounts of urea, and certain salts. 



In certain invertebrates (earthworms, planarians, et al.) the respiratory 

 gases pass through the skin. 



