66 CHEMICAL CONSTITUENTS OE BODY AND FOOD. 



and Lieberiiiann's artificial imclein. Altinann 1 showed that the 

 nitrogenous bases just alluded to originate from a complex organic acid, 

 which he termed nucleic acid, and that the true nucleins differ from one 

 another in the relative quantities of proteid and nucleic acid which they 

 contain. Nucleic acid is free from sulphur, and is in fact identical with 

 Miescher's imclein from spermatozoa. Miescher's formula for this 

 sulphur -free material was C 29 H 49 N 9 P 3 22 . Kossel's is C 30 H 32 N 9 P 3 17 . 

 More recent investigations by Miescher, 2 which were not published 

 until quite recently (after his death), by Schmiedeberg, led him to adopt 

 the formula C 40 H 54 N 14 17 (P 2 6 ) 2 for nucleic acid. He further considered 

 that in the spermatozoa, this acid is united to protamine. An exami- 

 nation of a preparation of nucleic acid, made from yeast by Altmann, 

 showed that here the formula was C 40 H 50 Ni 6 O 22 (l\O f> ) 2 (see further 

 under " Spermatozoa "). Nucleic a^id does not give the proteid reactions. 

 The relative amount of nucleic acid in different nucleins can be roughly 

 determined by micro-chemical reactions with aniline dyes, nucleic acid 

 having a great affinity for basic dyes like methyl-green. 3 



Hoppe-Seyler's classification of nucleins is the following : 



1. Nucleins like those found in spermatozoa, which contain no proteid, 

 but consist only of nucleic acid. 



2. The true nucleins, those found in cell nuclei. They yield proteid, 

 xanthine or alloxuric bases (hypoxanthine, xanthine, guanine, adenine), 

 and phosphoric acid. Those richest in nucleic acid occur in the chro- 

 matic fibres of the nucleus ; poorer in nucleic acid are the nucleins which 

 occur in the nucleoli (e.g. pyrenin), and which constitute the chief bulk 

 of the substance called plastin by histologists ; these are comparatively 

 insoluble in alkalis. They form numerous links in a chain which passes 

 insensibly into the group of the nucleo-proteids. 



3. The para-nucleins (or pseudo-nucleins) ; these are the nucleins 

 obtainable from nucleo-proteids (caseinogen, vitellin, cell nucleo-proteids). 

 They yield (like Liebermann's artificial nuclein) no nitrogenous bases, 

 but only proteid and phosphoric acid on boiling with water or dilute 

 acid. The nucleo-proteids of cell protoplasm can only be provisionally 

 included in this group; they contain so little nuclein, that even if 

 xanthine bases were obtained from these (and the point does riot seem 

 to have been thoroughly investigated yet) the small yield might escape 

 detection. The nucleo-proteid from muscle yields some of these bases 

 (see " Chemistry of Muscle "). 



There are at least four nucleic acids. They are compounds of an acid with 

 various bases, such as adenine, hypoxanthine, guanine, and xanthine. They 

 differ in the amount and character of the bases, and in the acid with 

 which these bases are combined. That from the thymus is called adenylic 

 acid (from the fact that its chief base is adenine). This, when heated with 

 sulphuric acid, yields a crystalline substance called thyxnin 4 (G 6 H 6 N 2 O 2 ), 

 cytosine, ammonia, levulinic acid, formic acid, and phosphoric acid. The 

 yield of cytosine, a new crystalline base (C 21 H 30 N ] [ 6 4 + 5H 2 0) amounts to 

 about 2 per cent, of the nucleic acid employed. The presence of levul- 

 inic acid among the products of decomposition is significant, and shows 

 that adenylic acid contains a carbohydrate group. This agrees with previous 



1 Arch.f. PhysioL, Leipzig, 1889, S. 524. See also Kossel, ibid., 1891. 

 z Arch.f. exper. Path. u. PhannakoL, Leipzig, 1896, Bd. xxxvii. S. 100. 



3 For a criticism of these microchemical methods, see Heine, Ztschr. f. physiol. C/iem., 

 Strassburg, Bd. xxi. S. 494. 



4 Kossel and Neumann, Ber. d. deutscJi. chem. Gesellsch.. Berlin, Bd. xxvi. S. 2753. 



