48 HUMAN PHYSIOLOGY 



(0 Adenin, C 5 H 5 N 5 . 



(tf) Hypoxanthin, C 5 H 4 N 4 O. 



These substances are closely related to each other. 

 Hypoxanthin is an oxidation product of adenin, xanthin is 

 an oxidation product of guanin and of hypoxanthin. They 

 are regarded as the precursors of uric acid or urea, for by the 

 reduction of uric acid xanthin and hypoxanthin can be pro- 

 duced. They are formed by the splitting up of nucleins 

 (see page 35). 



They are found in small quantities in urine, blood and the 

 organs, especially the liver and spleen. Their excretion is 

 increased during leukaemia. 



5. Hippuric acid (Benzoylglycocoll), 



C 6 H 5 .CO.NH.CH 2 .COOH, 



is found in the urine of plant-eaters. It is formed in the 

 kidneys by the synthesis of benzoic acid, C 6 H 5 .COOH, and 

 glycocoll, NH 2 CH 2 .COOH. 



6. Kreatin and kreatinin. 



Kreatin, C 4 H 9 N 3 O 2 , is methylguanidin-acetic acid: 



NH " 



^\N(CH 3 )-CH 2 -COOH. 



Guanidin is imido-urea: NH = C(NH 2 ) 2 . 

 Kreatinin, C 4 H 7 N 3 O, is the anhydrid of kreatin: 



/NH-CO 

 NH - C< \ 



\N(CH 3 )-CH 2 . 



Kreatin can be synthetically formed from cyanamid and methyl- 

 glycocoll (sarcosin) : 



y NH 2 



Co +NH(CH 3 ).CH 2 .COOH = NHzC< 

 XX NH X N(CH 8 ).CH 2 .COOH. 



Kreatin and kreatinin crystallize in monoclinic prisms. Both 

 are soluble in water. The reaction of kreatin is neutral, that of 

 kreatinin, alkaline. By the action of alkalies both form decom- 

 position products, among others, urea. 



