98 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



in vegetable food, but as it does not disappear in starvation, 

 some must arise from a particular phase of protein metabolism, 

 possibly the nucleins. 



The following is the procedure employed for its isolation: 

 The urine is acidified (20 c.c. of HC1 sp. gr. 1.12 for every 

 1000 c.c.) and extracted with a 10 per cent solution of alcohol 

 in ether. Three extractions are united, evaporated to 10-20 

 c.c., filtered and the filtrate made slightly alkaline with 

 NH 4 OH; to this is added a few c.c. of 1 per cent CaCl 2 solu- 

 tion and the mixture is rendered faintly acid with acetic 

 acid. Collect the precipitate on a small filter and examine 

 it under the microscope. Heat some on a platinum foil. 



HIPPURIC ACID, C 6 H 6 -CO-NH-CH 2 -C/Q H 



This substance is formed in the renal cells by a syn- 

 thesis of benzoic and aminoaceticacid or glycocoll. Normally 

 it is present as a hippurate to the amount of 7 grm. in 

 24 hours. The quantity is markedly augmented when ben- 

 zene derivatives such as exist in plants and fruits are inges! ed. 

 An increase in amount may also result from excessive putre- 

 faction of vegetable material in the intestine. Thus it is that 

 larger quantities of hippuric acid are always found in the 

 urine of herbivora than in that of carnivora. It readily crys- 

 tallizes in long rhombic prisms or needles formed in rosettes, 

 and is soluble in water and alcohol. If urine containing 

 hippuric acid is acidified. (20-30 c.c. of cone. HC1 to the liter) 

 and evaporated on the water-bath to a small volume, crystals 

 of this substance will form upon cooling. They may be col- 

 lected on a filter and washed- with a little alcohol saturated 

 with ether. 



(a) Heat a few crystals in a dry test-tube. They will 

 melt at 187 C., and at still higher temperatures will decom- 



