URINE 159 



of nucluin, the principal constituent of the nuclei. This therefore 

 leads us next to study : 



Purine Substances. Emil Fischer has shown that the decom- 

 position products of nuclein are derivatives of a substance he has 

 named purine. The empirical formulae for purine, the purine bases, 

 and uric acid are as follows : 



Purine . . C 5 H 4 N 4 



Hypoxanthine . C 5 H 4 N 4 Monoxypurine \ 



Xanthine . . C 5 H 4 N 4 O 2 Dioxypurine | Purine 



Adenine . . C,-jH 3 N 4 .NH2 Amino-purine j bases. 



Guanine . . C 5 H 3 N 4 O.NH 2 Amino-oxypurine/ 



Uric acid . . C- ) H 4 N 4 3 Trioxypurine 



There are a vast number of purine derivatives, but only a few 

 of them have at present any physiological importance. Others in 

 addition to those already enumerated are theophylline (dimethyl- 

 xanthine), theobromine (also a dimethyl -xanthine), caffeine (trimethyl- 

 xanthine) ; these are of interest, as they occur in tea, cocoa, and coffee. 

 A few words more may be added in respect to those in our list. 



Purine itself has never been discovered in the body. It has the 

 following structural formula : 



N=C-H 



H - C C - NH V 



II II ^ C ~ H 



N -C-N r 



The purine nucleus is depicted in the next formula, and its atoms 

 have been empirically numbered as shown for convenience of 

 description : 



5 C- 



4-4- 



Hypoxanthine or Sarcine is found in the body tissues and fluids, 

 and in the urine. It is derived from some nucleins, especially 

 those from fishes' spermatozoa. It may be termed 6-oxypurine, 

 as the oxygen is attached to the atom number 6 in the purine 

 nucleus. 



Xanthine is found with hypoxanthine in the body, and has been 

 obtained from a number of nucleins (from spermatozoa, thymus, 



