554 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



xanthin) probably loses its labile 3-methyl in the body, and occurs in the urine as 1-methyl- 

 xanthin. In like manner theobromin (3, 7-dimethylxanthin) is converted into heteroxan- 

 thin (7-methylxanthin). Caffein (I. 3, 7-trimethylxanthin) also parts with its 3-metbyl- 

 radicle and appears in the urine as paraxanthin (1, 7-dimethylxanthin). Kriiger and 

 Salomon 1 find 22. :: errams of heteroxanthin, 31.3 grams of l-methylxanthin, and 15.3 grams 

 of para-xanthin in L0,000 liters of urine, or much more in quantity than the true nuclein 

 bases (xanthin. etc.). 



That theophyllin, theobromin, and caffein may be demethylated in the tissue is an 

 interesting commentary on the methylation of tellurium, selenium, and pyridin by the 

 tissues. 



(d) MONOAMINOPURINS. 



N = C — XH, 



I I 

 Adenin, or 6-Aminopurin, H — C C — NH\ 



II II C-H. 

 X — C — X 



Adenin is found in the blood, the tissues, and the urine. It is especially a 

 decomposition product of thymus nuclein, although other nucleins may con- 

 tain it. Nitrous oxide converts it into hypoxanthin. 



(e) Amlnoxyptjrins. 



NH- C=0 



I I 

 Guanin, or 2-Amino-6-Oxypurin, H 2 N — C C — NH\ 



II II C-H 

 N C— N S 



This also is found as a decomposition product of some nucleins, especially 

 that of the pancreas. Combined with calcium it gives the brilliant irides- 

 cence to fish-scales. 2 It is found in the fresher layers of guano, and, accord- 

 ing to Voit, is here very probably derived from the fish eaten by the water- 

 fowl. • 



Epiguanin, or 7-Methyl-g-uanin. — This has been found in the urine, and like the 

 other methylated purins may very likely Vie derived from the fund fed. 3 



Episarcin is a purin hase which has been found in the urine, but whose configura- 

 tion has nol yel been made out. 



Carnin is said to occur in the urine. Its composition is unknown. 



(/) Trioxypurins. 



NH— C - O 



/ I 



Uric Acid, O = C C— XH 



>CO. — This acid is found in the nor- 

 MI_( _xh 



mal urine in small amounts, and may be detected in the blood and tissues, 



1 Zeitschriftfiir physidogische Chemie, 1898, Bd. 26, S. 350. 



2 Voil : Zeilschrifi fur wtssensehaftliche Zodlogie, Bd. 15, S. 515. 



' Kriiger and Salomon: Zeitschriftfiir physiologische Chemie, 1898, Bd. 26, S. 389. 



