174 THE PROTEIN SUBSTANCES. 



In preparing a pseudonuclein, dissolve the mother-substance in hydro- 

 chloric acid of 1-2 p. m., filter if necessary, add pepsin solution, and allow 

 the mixture to stand at the temperature of the body for about twenty- 

 four hours. The precipitate is filtered off, washed with water, and 

 purified by alternately dissolving in very faintly alkaline water and repre- 

 cipitating with acid. 



Plastin. After the extraction of the nucleins from cell nuclei of certain plants 

 by dilute soda solution, a residue is obtained which is characterized by its great 

 insolubility. The substance which forms this residue has been called plastin. 

 This substance, of which the spongioplasm of the body of the cell and the nucleus 

 granules are alleged to be composed, is considered as a nuclein modification of 

 great insolubility, although its nature is not known. 



Cleavage Products of the Nucleoproteins. 

 i. The Nucleic Acids. 



All nucleic acids are rich in phosphorus and yield phosphoric acid, 

 purine bases and a carbohydrate or carbohydrate derivative, as cleavage 

 products. Certain of them also contain pyrimidine bases. Not only 

 do the nucleic acids differ among themselves in regard to the occurrence of 

 different purine bases, but the opinions of authorities concerning this dif- 

 ference are conflicting. This last is perhaps due to the fact, which is now 

 admitted, that the two purine bases xanthine and hypoxanthine can be 

 produced secondarily from guanine and adenine. The statements as to 

 the occurrence of more than two purine bases in a nucleic acid require 

 further confirmation. There is no doubt that the most thoroughly 

 studied nucleic acids, such as the thymus-nucleic acids, the closely related 

 or perhaps identical acids of the salmon sperm (salmo-nucleic acid), of 

 the herring sperm and burbot sperm, and of the pancreas, do not contain 

 more than two purine bases, namely, guanine and adenine. 



Guanylic acid and inosinic acid contain only one purine base, namely 

 guanine and hypoxanthine respectively. The simplest nucleic acids also 

 contain no pyrimidine bases, which otherwise are found thus far in all 

 carefully investigated nucleic acids. Not all the nucleic acids are the 

 same in respect to the pyrimidine bases they contain. Although 

 thymine, cytosine and uracil are regularly obtained, and it is known that 

 the uracil can be produced secondarily from the cytosine, still the plant 

 nucleic acid, the triticonucleic acid, yields only cytosine and uracil, but 

 no thymine according to OSBORNE and HEYL/ who are confirmed by 

 WHEELER and JoHNSON. 2 LEVENE and MANDEL S have also found 

 cytosine and uracil, but no thymine, in the nucleic acid from the eggs of 

 the haddock. 



1 Amer. Journ. of Physiol., 21. 



2 Amer. Chem. Journ., 29. 



3 Zeitschr. f. physiol. Chem., 49. 



