37 PHYSIOLOGICAL CHEMISTRY. 



PROTEINS. 



As in the case of the sugars so with the proteins; there is 

 good evidence that traces of these nitrogen compounds are 

 normally present in the urine. ,The amount which may be so 

 present is, however, very small, in the mean not over 40 to 50 

 milligrams per liter. With these traces it is not possible to 

 say how many different kinds of proteins may occur, but the 

 serum albumin is doubtless the most abundant. With greatly 

 increased amounts of albumin in the diet the excreted albumin 

 is also increased, with no visible impairment of the kidney 

 mechanism. It is also true that foreign albumins injected into 

 the blood circulation, white of egg for example, are speedily 

 eliminated by the kidneys. 



Pathologically, however, the serum albumin and serum 

 globulin of the blood may pass through the kidneys in consid- 

 erable quantity. This is occasionally due to disturbances in 

 the circulation which may bring about an increase of blood 

 pressure, but ordinarily is due to structural changes in the kid- 

 neys themselves, through which the power of perfectly retain- 

 ing albumins of the blood is lost. A discussion of the nature 

 of these changes is not within the scope of this book, and for 

 an explanation of the tests which are employed in recognizing 

 the proteins of the urine the reader is referred to works on 

 urine analysis. Many of these tests are but modifications of 

 the delicate protein tests described in one of the earlier 

 chapters. 



URINARY SEDIMENTS. 



The urine when passed is usually clear, but frequently it 

 soon becomes cloudy and deposits a precipitate. This precipi- 

 tate may consist of a variety of constituents and may be due 

 to several causes. Sooner or later all urines, unless specially 

 protected by preservatives, undergo the so-called ammoniacal 

 fermentation in which urea is converted into ammonium car- 

 bonate by one of several bacteria. When this alkaline condi- 

 tion is reached the condition of equilibrium in which the vari- 

 ous salts exist together is destroyed and insoluble products are 



