170 THE URINE. 



insoluble salt with two bases, NH 4 MgP0 4 . In urinary 

 analysis it is referred to as triple phosphate. It is crystal- 

 line, sometimes in the form of snow-flakes, but more com- 

 monly in prismatic crystals often spoken of as "coffin-lid 

 crystals," from their supposed resemblance to the lid of a 

 coffin. (Plate II, 8.) 



The phosphoric acid of the urine is mainly that taken 

 in the food, but a part conies from the oxidized phos- 

 phorus compounds of the tissues, such as lecithin and the 

 nuclein compounds. The presence of a sediment of the 

 earthy phosphates shows simply that the urine is alkaline, 

 and is no indication that an excessive amount is being ex- 

 creted. Animal foods are richer in phosphoric acid com- 

 pounds than vegetable; hence with these we find more in 

 the urine. 



Experience has shown that there is a diminution of 

 the excreted phosphoric acid in many pathological condi- 

 tions. This is true in most acute infectious diseases, in 

 nephritis, gout, and rheumatism. In diabetes mellitus 

 there is an increase. Still, with the exception of the bones, 

 the tissues of the body contain but comparatively small 

 amounts of phosphorus compounds, and with our present 

 knowledge it is difficult to draw definite conclusions re- 

 garding the decomposition of such tissues from the varia- 

 tions in the eliminated phosphoric acid. 



367. Make a specimen of urine alkaline with sodium 

 hydrate. The earthy phosphates are precipitated in an 

 amorphous form. Examine under the microscope. See 

 that they are dissolved again by acidifying with even a 

 weak acid, like acetic. 



3G8. Filter out the earthy phosphates and test the 

 filtrate for the phosphoric acid of the alkaline phosphates 



