THE NUCLEINS. 57 



2. The second class is decomposed by dilute acids or 

 alkalies, giving, besides phosphoric acid and an albumin, 

 one or more of the nuclein bases, also called xanthin bases, 

 or purin bases, xanthin, guanin, etc. These nucleins are, 

 then, combinations of albuminous substances with nu- 

 cleinic acids. This class is found principally in the nucleus 

 of the cell and has been called nuclear, or nucleous nu- 

 cleins. 



The nucleins are not attacked by gastric juice, and 

 this is used to separate them from the albuminous com- 

 pounds, which can be digested by it. They are insoluble 

 in water and dilute acids, but soluble in alkalies. They 

 give the biuret and Millon's tests in consequence of the 

 albumin which they contain. 



134. Mix 50 grammes of compressed or brewers' yeast with 

 200 grammes of water, and allow the yeast to subside. Pour 

 off the water and to the residue add O.o-per-cent. potassium 

 hydrate solution; stir, and, after waiting a few minutes to dissolve 

 the nucleins, filter and acidify with hydrochloric acid. Filter out 

 the precipitated nucleins, wash with HC1, then hot alcohol. Dry 

 over sulphuric acid. Try solubility in acids and alkalies, also biuret 

 and Millon's tests. The residue gained by fusion with sodium car- 

 bonate and potassium nitrate gives a yellow precipitate with am- 

 monium molybdate, showing the presence of phosphoric acid. 



A few of the nucleins, both animal and vegetable, contain 

 iron, and these are the principal source of the iron in the animal 

 body, our food-materials containing no inorganic compounds of 

 iron. Hsematogen is an. example of such nucleins. It is found in 

 the yelk of hen's eggs united with an albuminous substance, 

 which can be split off by digestion. 



The iron in such organic combinations as nuclein does not 

 respond to the ordinary chemical tests until the compound has 

 been decomposed by chemical agents or other means. Reagents 

 like ammonium sulphid and potassium ferrocyanid decompose 

 it very slowly, whereas they act immediately upon the inorganic 

 compounds of iron and not at all upon hsematin. The nucleins 



