THE CHEMISTRY OF THE ANIMAL BODY. 579 



Nucleo-proteids, or Nucleo-albumins ' and Nucleic Acids. — These are compounds 

 of proteid with nuclein, which latter yields phosphoric acid on decomposition. If nucleo- 

 proteid, which is found in every cell, be digested with pepsin-hydrochloric acid, there remains 

 a residue of insoluble nuclein, which is likewise insoluble in water but soluble in alkalies. 

 If this nuclein yields xanthin bases on further decomposition, it is called true nuclein; if it 

 fails to yield these bases, it is called paranuclein or pseudonuclein. Nucleo-proteids 

 yielding proteid and paranuclein on decomposition include the casein of milk, pyin of 

 the pleural cavity, vitellin of the egg, Bunge's iron-containing hsematogen of the egg, 

 as well as nucleo-proteids found in all protoplasm. They all contain iron. Paranuclein 

 is probably absorbable (see p. 514). Casein yields on peptic digestion phosphorized 

 albumoses from which paranuclein is split : this cleavage is followed by the further 

 digestion of the albumose and the gradual solution of the paranuclein.-' Kobrak 3 shows 

 that woman's casein has two-thirds the acidity of cow's casein, but that the former dis- 

 solved and reprecipitated six times has the same properties as the latter. He believes that 

 woman's casein may consist of cow's casein united with another product of more basic 

 properties. 



A second group of nucleo-proteids yields true nuclein on decomposition. This true nuclein 

 is a modified form of the original nucleo-proteid, and consists of nucleic acid in combination 

 with proteid. On decomposition the nuclein breaks up into its constituent proteid and nucleic 

 acid, which latter always yields one or more of the xanthin bases, which arc. therefore, 

 called nuclein bases. The nucleic acid is similar to that derived from sperm, which is 

 combined with protamin in the sperm nucleus. The nucleic acid of yeast nuclein yields 

 guanin and adenin, that of a bull's testicle adenin, hypoxanthin, and xanthin, that of the 

 thymus adenin and guanin, that of the pancreas guanin alone. The latter has been 

 termed " guanylic acid," and "adenylic" and "xanthylic" acids may also be considered 

 individual nucleic acids. Each one of this family of acids has the power of combining 

 with any soluble proteid to form nucleo-proteid, hence there may exist a large variety 

 of nucleo-proteids. And the variety is further increased by the diversity of other decom- 

 position products yielded by the various nucleic acids. Thus most nucleic acids yield 

 thymic acid, which, however, cannot be found in pancreas nucleo-proteid. A crystalline 

 base called cytosin has been discovered in thymus nucleic acid. Some nucleic acids, like 

 that derived from yeast, readily yield carbohydrates (a hexose and a pentose) : while others, 

 like thymus nucleic acid, show the presence of the carbohydrate group only in the pro- 

 duction of levulic acid after very thorough decomposition ; and still others (salmon sperm) 

 fail to indicate the presence of any carbohydrate radicle. According to Kossel, nuclei 

 may at times contain free nucleic acid. According to Bang, 4 nucleic acid may unite in 

 three ways: with protamin, as in sperm nucleic acid; loosely with proteid, as in most 



nucleo-proteids; and strongly with proteid, as in pancreas nucleo-proteid. Thelast-nai 1 



pancreas nucleic acid yields guanin on decomposition, and has been termed "guanylic 

 arid." Bang gives the following analysis : guanin, 36 percent, (containing nine-tenths 

 of all the nitrogen present); a little ammonia; a pentose, 30 per cent., and I '_(),. I7.»'. 

 per cent. The rest unaccounted for is 17.5 per cent. 



Phospho-glyco-proteids. — This class is represented by Hammarsten's hdico-proteid, 

 which yields paranuclein. and, unlike other nucleo-proteids of the paranuclein class, it 

 yields a reducing carbohydrate on boiling with acids. 



The Albuminoids. -These are bodies derived from tine proteid in the body, but nol 

 themselves convertible into proteid. They are resistant to the ordinary proteid solvents, 

 and as a rule exist in the solid state when in the body. 



1 These two terms arc used here as synonymous, though Hammarsten would confine the 

 term nucleo-albmnin to those proteids which yield paranuclein. 



2 Salkowski: Zeitschrift fur physiologische <'li'ini<\ 189!*, I'll. 27, 8. 297. 

 » I'lirnjrrx Archiv, 1900, P.d. 80, S. 69. 



* Zeitschrift fiir physiohgisehe Chemie, 1898, Bd. 26, S. 133. 



