108 PHYSIOLOGICAL CHEMISTRY 



process of cell division, and thus in reproduction and growth, 

 any substances found regularly and characteristically in the 

 nucleus will be of great interest. The nucleoproteins are char- 

 acterized by containing nucleic acid, which may be obtained from 

 them by splitting off the protein portion of the molecule. This 

 process can be carried on in two stages, part of the protein split- 

 ting off more easily, leaving a product called nuclein, as in the 

 action of gastric juice on a nucleoprotein. By the action of 

 caustic alkali the remaining protein in nuclein may be split off, 

 leaving nucleic acid. 



This nucleic acid is by far the more interesting part of the 

 nucleoprotein molecule, and it has been much studied. By 

 vigorous hydrolysis nucleic acid may be split into four kinds of 

 material (1) purine bases, (2) pyrimidine bases, (3) a carbohy- 

 drate, and (4) phosphoric acid. Four purine bases are obtained, 

 adenine, guanine, hypoxanthine and xanthine. Only the first 

 two are considered to be present in the original molecule, the 

 last two being formed from the others in the process of hydro- 

 lysis. In the body a fifth member of the group is formed from 

 the others, uric acid. 



HN = 



I I 

 = NH 



= 



NH NH 

 Uric Acid. 



The pyrimidine bases are somewhat closely allied to the 

 purine bases. Uracil, thymine and cytosine are the three mem- 

 bers of the group obtained from nucleic acid. 



The carbohydrate portion of the nucleic acid is sometimes a 

 pentose and sometimes a hexose or allied substance. 



The fourth product is phosphoric acid, H 3 P0 4 . 



The structure of the nucleic acids has been worked out, and 

 the student is referred to larger works for further discussion of 

 this subject. 



