SECRETION. 431 



the offensive sweat of feet there are found leucin, tyrosin, valerianic 

 acid, and ammonia. 



THE SECRETION OF THE URINE. 



In a perfectly normal being the problems of waste and repair 

 are balanced to a nicety. This equilibrium owes its maintenance to 

 the proper action of the various glands of the economy, whether secre- 

 tory or excretory. As we know, the tissues of the body are bathed in 

 lymph containing in solution the compounds that are necessary for 

 their nourishment: proteids, carbohydrates, fats, salts, and gases. 

 By reason of the organism exercising its various functions, waste 

 follows in direct proportion to the activity of the tissues. The worn- 

 out and effete materials first find their way into the lymph and from 

 it into the blood-stream, to be later eliminated from the economy, 

 else deleterious results will follow their retention in the body. It is 

 by the selective action of the cells of the various glands of the body 

 that these useless substances are removed from the blood : that is, 

 secreted by them and converted into such form as to be readily re- 

 moved to the exterior of the organism by excretory processes. In the 

 main, the products to be removed are urea and allied nitrogenous 

 bodies, carbon dioxide, salts, and water. Most of the water, salts, 

 urea, and allied substances are eliminated as components of the urine 

 by those most important organs, the kidneys. These organs are of 

 vital importance, since nearly all of those waste-products containing 

 nitrogen are eliminated in the urine. 



The kidneys secrete the urine. Their excretory functions, a mat- 

 ter oi everyday observation, represent the extent of their external 

 secretion ; although not yet definitely settled, the consensus of opinion 

 leans toward the kidneys possessing an internal secretion as well. 



Morphology of the Urinary Apparatus. The secretory organs of 

 the urine are the kidneys. They, two in number, are compound tubu- 

 lar glands, situated in the back part of the abdomen. The kidneys 

 are extraperitoneal organs, lying behind the peritoneum and resting 

 upon the lumbar portion of the diaphragm and the anterior layer of 

 the lumbar fascia. The upper borders of the kidneys touch a plane 

 that is on a level with the upper border of the twelfth dorsal vertebra ; 

 their lower extremities are on a level with the third lumbar vertebra. 

 The right kidney is usually somewhat lower than the left, probably 

 because of the pressure exerted by the liver, against whose lower sur- 

 face the kidney rests. In front it is in relation with the liver, the 

 descending portion of the duodenum, and the hepatic flexure of the 



