98 THE CLEAVAGE PRODUCTS OF THE NUCLEOPROTEWS. 



nucleinic acid apparently represents a product intermediary between 

 thyminic acid and the original substance. Its formula is given as 

 CigHgjNgPgOgo. It still contains nucleinic bases, one or more carbo- 

 hydrate groups, and possibly ammonia. According to Ascoli, the 

 substance also contains iron in masked form. 



The phosphorus of the nucleinic acids is possibly present in a form 

 analogous to the polymetaphosphoric acids ; Schmiedeberg suggests 

 pyrophosphoric acid as a possibility. 



According to Kossel, at least two different carbohydrate complexes 

 may occur in the nucleinic acids, viz., 1, a pentose, which has been 

 shown to be ^-xylose, first demonstrated in yeast nucleinic acid and 

 later shown to be a common complex of the various nucleinic acids ; 

 2, a reducing hexose, which on decomposition yields laevulinic acid 

 and formic acid ; this was found in the thymonucleinic acid, and 

 later in that obtained from the spermatozoa of the sturgeon. In 

 tritico-nucleinic acid Osborne and Harris obtained evidence of three 

 pentose groups, while a hexose was absent. 



Whether or not all nucleinic acids contain a pentose group has 

 been rendered somewhat doubtful by Bang's statement that this is 

 absent in thymo-nucleinic acid. He adds that the thymus itself 

 contains considerable quantities of a pentose. 



The basic decomposition-products of the nucleinic acids, as has 

 been mentioned, are the common purin bases xanthin, hypoxanthin, 

 guanin, and adenin ; and the pyrimidin derivatives cytosin, uracil, 

 and thymin. These will be considered below. 



There remains an unresolved residue, of which nothing is known. 

 To what extent this is concerned in the production of melanins or 

 melanoid substances, which are constant decomposition-products of 

 the nucleinic acids (Schmiedeberg, Osborne, and Harris), remains to 

 be seen. 



The Pyrimidin Derivatives of the Nucleinic Acids. 



The pyrimidin derivatives of the nucleinic acids are cytosin, 

 uracil, and thymin. 



Cytosin. Cytosin is apparently a constant decomposition-product 

 of all nucleinic acids. It has been obtained from thymo-nucleinic 

 acid, from the spermato-nucleinic acid of the sturgeon and herring, 

 from the nucleinic acid of the spleen, the liver etc. Its formula is 

 C 4 H 5 N 3 O ; structurally it is 6-amino-2-oxy pyrimidin : 



If we compare with this the structure of the purin bases, and 

 notably of uric acid, which is a constant oxidation-product of the 

 purin bases and formed synthetically from pyrimidin derivatives 



