206 



ELEMENTARY BIOLOGY 



is to that extent impeded, and the whole body suffers in conse- 

 quence of the retention of urea and other poisonous by-products 



of protoplasmic activity. 



239. Hygiene of the skin. 

 The skin is more than an ex- 

 creting organ ; indeed, the 

 excretory work of the skin 

 may be considered rather in- 

 cidental. Other functions of 

 the skin are as follows : 



1. Protection of the body 



(a) against mechanical injury, 



(b) against drying up, and (c) 

 against excessive radiation of 

 heat. 



2. Regulation of the body 

 temperature. 



3. Perception of sensations 

 of touch, heat, etc. 



But it is the secretions of 

 the fat glands and the perspi- 

 ration (see Fig. 77) that give 

 rise to the need for special 

 attention to the skin. 



The accumulation of wastes 

 left behind when the perspira- 

 tion evaporates and the catching of dust in the oil secreted by 

 the oil glands, and in the pores through which the oil is secreted, 

 call for periodic bathing. The best way to remove the accu- 

 mulated wastes and dirt is by means of hot water and soap, 

 with the help of a brush. But hot baths have a debilitating 

 effect, forcing the blood into the capillaries of the skin and thus 

 away from the muscles, brain, and internal organs. A warm bath 

 once or twice a week should be enough for ordinary cleanliness 

 if these supplement a daily cold bath. 



FIG. 78. Kidneys and bladder 



a, the main artery, and &, the main vein, in 

 the abdominal cavity, giving off branches 

 to the kidneys, cc ; d, funnel-shaped cavity 

 in which the waste fluid is gathered by the 

 gland action of the kidney ; ee, tubes lead- 

 ing from the kidney to the bladder, /. The 

 left kidney is represented as cut through 

 lengthwise 



