30 



ESSENTIALS OF CHEMICAL PHYSIOLOGY 



nucleic acid, together with a variable amount of proteid. Nucleic 

 acid on decomposition yields phosphoric acid and various bases of 

 the xanthine group. Some forms of nuclein, called pseudo-nuclein, 

 such as are obtained from casein and vitellin, differ from the true 

 nucleins in not yielding these xanthine or, as they are sometimes 

 termed, alloxuric or purine bases. 



Further particulars concerning the alloxuric bases will be given 

 under Ueic Acid, to which they are closely related. 



The following diagrammatic way of representing the decomposi- 

 tion of nucleo-proteid will assist the student in remembering the 

 relationships of the substances we have just been considering : — 



Nucleo-Proteid 

 subjected to gastric digestion yields 



Proteid converted into 

 peptone, which goes 

 into solution. 



Proteid — converted into 

 acid albumin in solu- 

 tion. 



Nuclein, which remains as an insoluble 

 residue. If this is dissolved in alkali 

 and then hydrochloric acid added it 

 yields 



A precipitate consisting of nucleic acid. 

 If this is heated in a sealed tube with 

 hydrochloric acid, it yields a number 

 of imperfectly known substances like 

 thymic acid and in some cases a re- 

 ducing sugar. But the best known 

 and constant products of its decom- 

 position are 



Phosphoric acid. 



Purine bases, viz 

 Adenine 

 Hypoxanthine 

 Guanine 

 Xanthine 



The nuclein obtained from the nuclei or heads of the spermatozoa 

 consists of nucleic acid without any proteid admixture. In fishes' 

 spermatozoa, however, the nucleic acid is united to protamine, the 

 chemical properties of which we shall be considering immediately. 



