266 THE HUMAN BODY. 



into the calices of the pelvis of the ureter, and this tube 

 then conveys it to the bladder. 



The Renal Secretion is less in bulk in warm weather, 

 when perspiration carries off a good deal of the excess 

 water of the blood, than in cold. On an average the kid- 

 neys eliminate from the body in twenty-four hours about 

 fifty ounces (2 pints) of water, and 500 grains (1% ounces) 

 of urea, which contain a little more than 230 grains of 

 nitrogen. 



The Kidneys, being the chief organs for the excretion 

 of nitrogen, are among the most important organs of the 

 body. Any defect in their healthy activity leads to serious 

 interference with the working of many organs, due to the 

 accumulation in the body of nitrogenous waste products.* 



The Skin, which covers the whole exterior of the body, 

 consists everywhere of two distinct layers: an outer, the 

 cuticle or epidermis; and a deeper, the dermis, cutis vera, 

 or corium. A blister is due to the accumulation of liquid 

 between these two layers. Hairs and nails are excessively 

 developed parts of the epidermis. 



The Epidermis, Fig. 75, consists of cells, arranged in 



Where does the ureter convey it? 



Is the bulk of the renal secretion greater in summer or in winter? 

 Why? What is its average daily amount? How much urea does it 

 contain? How much nitrogen is contained in this quantity of urea? 



Why are the kidneys important organs? What follows when 

 their physiological work is defective? 



Of what two main parts does the skin consist? What is a blister? 

 What are hairs and nails? 



* BrighVs Disease, one of the commonest and most dangerous of maladies, 

 consists essentially in an alteration of the kidney structure, in consequence of 

 which these organs cease to eliminate urea from the blood, and drain off pure 

 albumen from it instead. The three most common causes of Bright's disease 

 are (1) an acute illness, as scarlet fever, of which it is a frequent result; (2) sud- 

 den exposure to cold when warm (this often drives blood in excessive amount 

 irom the skin to internal organs and leads to k ; dney disease); and (3) excessive 

 drinking of alcoholic liquids. 



