76 PHYSIOLOGY 



The pyrimidine bases which are also obtained from the hydrolysis 

 of nucleic acid are derived from a pyrimidine nucleus which is, so to 



/ N 



speak, half a purine nucleus, consisting of a C\ chain joined to a 



X N 



3-carbon chain. Three pyrimidine bases have been isolated from the 

 decomposition products of nuclein, namely, thymine, cytosine, and 

 uracil. 



NH CO NH CO N = O.NH 3 



CO CH CO C.CH 3 CO CH 



I II I II I II 



NH CH NH CH NH CH 



Uracil 2-6-dioxy- Thymine 5-mcthyl- Cytosine 6-amino- 



pyrimidine uracil 2-oxypyrimidino 



Cytosine is easily converted by oxidation into uracil. 



After separation of the purine and pyrimidine bases and phosphoric 

 acid a substance is left over which gives the reactions of a carbo- 

 hydrate. This carbohydrate residue differs in different nucleic acids. 

 The only one which has been so far isolated is a pentose, namely, 

 /-xylose. It is stated that the nucleic acids of yeast and of the thymus 

 gland yield a hexose. In most cases it is impossible to say how far 

 these different bodies are combined to make up nucleic acid. From 

 muscle an acid of the same class, inosinic acid, can be extracted which 

 yields crystalline barium and calcium salts. This has been found to 

 consist of one molecule each of hypoxanthine, xylose, and phosphoric 

 acid. According to Neuberg, it has probably the following constitu- 

 tional formula : 



(1) HN (6) CO 



CH 9 OH 



