CHAPTER XI 

 URINE 



General. The body is by no means a permanent structure 

 if considered from the standpoint of the individual molecules of 

 which it is composed. The tissues are constantly wearing out 

 and being rebuilt in the process of wear and tear. In this 

 process waste products are formed. For the maintenance of 

 body temperature and the performance of mechanical work, sub- 

 stances are constantly being ''burned" or oxidized in the body, 

 both substances from the food, or from the organic reserves of 

 the tissues themselves. Here also waste products are produced. 

 The body must dispose of waste material. This is accomplished 

 by way of the various excretions, through skin, lungs and 

 kidneys, and in the feces. 



The skin excretes water and salts, and about a gram of nitro- 

 gen per day in various compounds. From the lungs much water 

 and carbon dioxide are given off. The feces contain mainly undi- 

 gested food residues, the dead bodies of intestinal bacteria and 

 substances from the digestive secretions, but also some other 

 materials which are excreted into the intestine. They contain 

 1-2 grams of nitrogen per day. 



Most of the nitrogen excreted is given off in the urine how- 

 ever, and hence this excretion attracts especial interest ; a study 

 of the amounts and variations in the nitrogen elimination often 

 will give valuable information as to what is going on in the body 

 itself. This is not confined entirely to nitrogen compounds, for 

 the urine contains various other substances of interest. Occa- 

 sionally also, abnormal constituents appear, and by their pres- 

 ence or amount give information which is of great value to the 

 physician. The study of the urine is thus of primary impor- 

 tance. 



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