254 



PRACTICAL PHYSIOLOGY 



Indie an Test. To about 5 c.c. of urine in a test tube add an equal 

 volume of concentrated hydrochloric acid and 3 c.c. of chloroform, 

 then add drop by drop a dilute (freshly prepared) solution of bleach- 

 ing powder. Shake the tube after the addition of each drop of 

 the hypochlorite solution. The pigment, as liberated, is taken up 

 by the chloroform. Care must be taken not to add too much of 

 the .bleaching powder, as the indigo blue formed can be further 

 oxidised to colourless compounds. 



In place of the bleaching powder, hydrochloric acid containing 

 a small amount of ferric chloride (0-2 to 04 per cent.) may be 

 used. Or it may be replaced by ammonium persulphate, say, 

 1 drop of a 10 per cent, solution. 



CHAPTER XIV 



URINE (Continued) 



Total Nitrogen and Urea 



The amount of total nitrogen excreted by the average man 

 living on an average mixed diet is about 15 grams per day. As the 

 amount of nitrogen excreted is dependent mainly on the nature of 

 the diet, it is obvious that no hard and fast figure can be laid down 

 for a mixed diet. And, further, unless a sample of a mixed twenty- 

 four hours collection is taken the values obtained are for the most 

 part absolutely worthless. Even a sample from the twenty-four 

 hours urine is of little value unless the nature of the diet consumed 

 during the period of collection is known. If a reliable sample of 

 urine is required, the subject must be put on a simple fixed diet for 

 at least two days before the twenty -four hour sample is collected. 



The chief nitrogenous substances present in the urine which 

 collectively account for the bulk of the total nitrogen (T.N.) are 

 urea, uric acid, ammonia and creatinine. Many other nitrogen 

 containing substances are present in the urine, but as a rule they 

 only occur in traces. Not only does the amount of total nitrogen 

 excreted depend on the nature of the diet, but, as Folin has shown, 

 the distribution of the component substances varies with the diet 

 taken. Folin's table demonstrates this fact very clearly. 



