66 CHEMICAL CONSTITUENTS OF BODY AND FOOD. 
and Liebermann's artificial nuclein. Altmann 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 nuclein from spermatozoa. Miescher's formula for this 
sulphur-free material was C 29 H 49 N 9 P 3 22 . Kossel's is C^H^N^O^. 
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 64 N 14 O 17 (P 2 O 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 5n N 16 O 22 (P 2 O-) 2 (see further 
under " Spermatozoa "). Nucleic acid 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-iiucleins) ; 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 not 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 thymin 4 (Cr ) H N. ) O : ,), 
cytosine, ammonia, levulinic acid, formic acid, and phosphoric acid. The 
yield of cytosine, a new crystalline base (C., 1 H ?0 jS t 10 O 4 + 5H./J) 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./. Physiol., Leipzig, 1889, S. 524. See also Kossel, ibid., 1891. 
- Arch. f. exper. Path. u. PharmakoL, Leipzig, 1896, Bd. xxxvii. S. 100. 
3 For a criticism of these mierochemical methods, see Heine, Ztschr. f. 2'hysiol. C'Icem., 
Strassburg, Bd. xxi. S. 491. 
4 Kossel and Neumann, Per. d. deutsch. diem. Grsellsch., Berlin, Bd. xxvi. S. 2753. 
