ELEMENTARY CHEMICAL PHYSIOLOGY 261 



is, however, of a dull brown colour instead of being yellowish red, as it usually 

 is. This is because a certain amount of the cuprous oxide unites with some 

 of the uric acid to form a brown compound. 



Hippuric Acid. This substance is found in marked amount in the urine of 

 herbivora, but is only present in small amount in the urine of man on an 

 ordinary mixed diet. It is chemically benzoyl-glycine and is formed from 

 aromatic substances present in the food, particularly vegetable food-stuffs, 

 being oxidised to benzoic acid which is then excreted combined with glycine. 



Creatinine. Urine always contains creatinine, the output on a 

 creatinine-free diet being very constant for a given individual. 

 Creatine is not normally present in the urine of the adult although 

 it is normally present in the urine of young children and is frequently 

 present in the urine of women at menstruation and in pregnancy. 

 It can be made to appear readily by starvation and it is excreted in 

 certain pathological conditions. 



Tests for Creatinine. EXPERIMENT I. Jaffe's Test. Add to 

 5 c.c. urine a few drops of a saturated solution of picric acid and then 

 NaOH until alkaline. A red brown colour is produced due to the 

 formation of picramic acid. Do a check observation on 5 c.c. 

 water. 



EXPERIMENT II. Weyl's Test. Add to 5 c.c. urine a few drops of a dilute 

 solution of sodium nitro-prusside, then on the addition of dilute caustic soda 

 solution a ruby red colour develops which quickly changes to yellow. If this 

 solution be acidified with acetic acid and then boiled a greenish blue colour 

 results and eventually on standing a precipitate of Prussian blue is formed. 



Acetone gives the same colour with the nitro-prusside and soda, but (1) it 

 does not turn yellow on standing, and (2) it gives a reddish purple colour 

 on the addition of acetic acid. 



Simple Estimation of Creatinine (Burns). Apparatus. Haldane's 

 Haemoglobinometer tubes. Standard tube contains the Folin 

 standard solution of bichromate (see p. 285). 



Method. Pipette 10 c.c. of urine into a 250 c.c. measuring 

 cylinder, add 5 c.c. 10 per cent. NaOH and 15 c.c. saturated solution 

 of picric acid. Mix and allow to stand for exactly six minutes. 

 Dilute with water to 250 c.c. Fill empty hsemoglobinometer tube 

 up to 50 mark with the mixture, add water drop by drop until the 

 colour of the mixture and the standard match. (It is better, as in 

 the estimation of haemoglobin, to note the point at which the colour 

 is just too strong and the point at which it is just too pale and take 

 the mean of these.) The reading gives the amount of creatinine 

 present in milligrams per 100 c.c. of urine. 



Ammonia. The amount of ammonia in urine varies indirectly 

 with the amount of urea, due to the fact that ammonia is the chief 

 precursor of urea. If for any reason, such as the presence of acids 

 in the body, ammonia is required for neutralisation, there will be a 

 rise in the output of ammonia in the urine and a fall in the urea 

 output. In certain pathological cases where acidosis is a marked 

 feature the ammonia nitrogen may form a large proportion of the 

 total urinary nitrogen. 



