URINE 



423 



FIG. 133. CALCIUM SULPHATE. 

 (Hensel and Weil.) 



filter paper saturated with lead acetate solution. In a short time the portion of 

 the paper in contact with the vapors within the test-tube becomes blackened due 

 to the formation of lead sulphide. The nascent hydrogen has reacted with the 

 loosely combined or neutral sulphur to form hydrogen sulphide, and this gas com- 

 ing in contact with the lead acetate paper has caused the production of the black 

 lead sulphide. Sulphur in the form of inorganic or ethereal sulphuric acid does 

 not respond to this test. (For discussion of neutral sulphur compounds see 

 page 409.) 



4. Calcium Sulphate Crystals. Place 10 c.c. of urine in a test-tube, add 10 

 drops of calcium chloride solution and allow the tube to stand until crystals form. 

 Examine the calcium sulphate crystals under 

 the microscope and compare them with those 

 shown in Fig. 133. 



Chlorides 



Next to urea, the chlorides consti- 

 tute the chief solid constituent of the 

 urine. The principal chlorides found 

 in the urine are those of sodium, potas- 

 sium, ammonium, and magnesium, with 

 sodium chlaftide predominating. The 



excretion of chloride is dependent, in great part, upon the nature of the 

 diet, but on the average, the daily output is about 10-15 grams, expressed 

 as sodium chloride. Copious water drinking increases the output of 

 chlorides considerably. Because of their solubility, chlorides are never 

 found in the urinary sediment. 



Since the amount of chlorides excreted in the urine is due primarily 

 to the chloride content of the food ingested, it follows that a decrease 

 in the amount of ingested chloride will likewise cause a decrease in the 

 chloride content of the urine. In cases of actual fasting the chloride 

 content of the urine may be decreased to a slight trace which is derived 

 from the body fluids and tissues. Under these conditions, however, 

 an examination of the blood of the fasting subject will show the per- 

 centage of chlorides in this fluid to be approximately normal. This 

 forms a very striking example of the care nature takes to maintain the 

 normal composition of the blood. There is a limit to the power of the 

 body to maintain this equilibrium, however, and if the fasting organism 

 be subjected to the influence of diuretics for a time, a point is reached 

 where the normal composition of the blood can no longer be maintained 

 and a gradual decrease in its chloride* content occurs which finally results 

 in death. Death is supposed to result not so much because of a lack of 

 chlorine as from a deficiency of sodium. This is shown from the fact that 

 potassium chloride, for instance, cannot replace the sodium chloride 



