THE SKIN AND THE KIDNEYS 



207 



kidneys, and a little over one ounce of urea. Out of the body, 

 the urea soon changes into carbon dioxide and ammonia. 



Besides urea, the kidneys also serve to carry off each 

 day almost an ounce of various mineral substances that are 

 either foreign to the body or 

 are present in the blood in too 

 large a proportion, for ex- 

 ample, common salt. 



If the kidneys are inactive 

 or fail to excrete the nitroge- 

 nous waste matters, the work 

 of many other organs is seri- 

 ously impaired. The blood 

 is poisoned, and death may 

 result from the poisonous 

 material which is retained in 

 the tissues. 



281. The Health of the Kid- 

 neys. The kidneys are very 

 busy organs. Their health is 

 a matter of prime importance. 



We have already become 

 familiar with the hygiene of 

 two great organs of excretion, 

 the skin and the lungs. 



These three sets of organs, 

 working together in harmony, 



like three groups of mechanics doing some difficult work, 

 keep the bodily machinery from getting clogged and choked 

 with waste matters. 



If the free action of the skin or the lungs is interrupted, 

 the kidneys have extra work to do. They make every effort 



FIG. 129. Vertical Section of the 

 Kidney. 



A, pyramids of the kidney ; B, apices, 

 or papillae, of the pyramids ; C, pel- 

 vis of the kidney; JD, upper end of 

 ureter. 



