56 THE NUCLEINS. 



133. Make a gastric juice by adding a few grains of pepsin 

 to 0.2-per-cent. HCI 1 and digest in it for some time at the tempera- 

 ture of the body some casein. The nucleoalbumin is decomposed 

 into two substances: an albumin, which is dissolved, and a 

 nuclein, a compound rich in phosphorus, which remains. Filter out 

 the nuclein, and test the nitrate with the biuret test for the 

 albuminous compound. 



THE NUCLEINS. 



The nucleins occur partly combined with albuminous 

 substances as nucleoalbumins, partly free in the nucleus of 

 the cell. They are composed of phosphoric acid united 

 with an albumin, or sometimes in addition with a nuclein 

 base, such as adenin, guanin, xanthin, or hypoxanthin. 

 Besides the elements found in vhe albumin they contain 

 phosphorus and sometimes iron. The iron in the haamo- 

 globin is probably obtained by the animal organism from 

 such compounds as these. We have no absolute proof that 

 the common salts of iron can be assimilated by the animal 

 organism. One of the nucleins which may furnish iron to 

 the animal body is haamatogen, found in the yelk of eggs. 

 The nucleins may be divided into two classes: 

 1. Those which, when acted on by hot acids or alka- 

 lies, take up water and give, as decomposition-products, 

 phosphoric acid and an albumin. They have been called 

 paranucleins or pseudo-nudeins. Such a one is contained 

 in casein. It can be set free by digesting with gastric juice 

 from the albumin with which it is united. Haamatogen is 

 also of this class, and probably furnishes the iron for the 

 haemoglobin of the young bird. 



1 This strength of acid can be obtained by diluting concentrated 

 hydrochloric acid with 150 times its volume of water. 



