MUSCULAR TISSUE. 33 



and heated, a green color is obtained, and upon continued 

 boiling a precipitate of Prussian blue settles out. 



(c) Jaffe's Reaction. Treat some of the solution with a 

 dilute solution of picric acid, and make it faintly alkaline 

 with NaOH. The solution immediately becomes a deep red 

 Acetone responds to this test, but gives merely a yellowish- 

 red color. 



PURINE BASES. 



(6) 



(1) 



(2) HC (5)C NI 



I I (7) 



C 



H (8) 



(3) N - C - 



(4) (9) 



This represents structurally the compound, purine, the 

 nucleus from which all the purine bases may be derived. The 

 structure of the bases is easily obtained by substitution in 

 the nucleus at the position indicated by number. 

 Hypoxanthine = 6-Oxypurine. 

 Guanine = 2-Amino-6-oxypurine. 

 Xanthine = 2,6-Dioxypurine. 

 Adenine = 6-Aminopurine. 



The purine bases in greater part exist as constituent groups 

 in the more complex nucleic acid molecule. In some tissues, 

 however, they have been found in the free state. They form 

 crystalline salts with the mineral acids and are all precipitated 

 from acid solutions by means of phosphotungstic acid. 

 Upon the addition of ammoniacal silver nitrate they sepa- 

 rate from their solutions as silver combinations. Copper 

 acetate combines with them to form insoluble compounds. 



The separation of the bases from the creatine filtrate (see 

 p. 31) takes place as follows: 



