176 THE PROTEIN SUBSTANCES. 



chloride and salts of the heavy metals, and as a rule insoluble basic salts 

 with the alkaline earths. The /3-guanylic acid is soluble with difficulty 

 in cold water but rather readily in boiling water, from which it separates 

 on cooling. Guanylic acid is readily precipitated from its alkali compound 

 by an excess of acetic acid. The other nucleic acids are, on the contrary, 

 not precipitated from such compounds by an excess of acetic acid, but 

 by a slight excess of hydrochloric acid, especially in the presence of alcohol. 

 In acid solutions these latter nucleic acids give precipitates with pro- 

 teins, which are considered as nucleins. The behavior of guanylic acid 

 in this regard has not been shown on account of the great difficulty in 

 dissolving it in dilute acids. All nucleic acids are insoluble in alcohol 

 and ether. They do not give either the biuret test or MILLON'S reac- 

 tion. The nucleic acids are optically active and indeed dextrorotatory 

 {GAMGEE and JONES 1 ). 



The proteolytic enzymes, such as pepsin and trypsin, decompose the 

 nucleoproteins more or less; the nucleic acids are not split by these 

 enzymes as far as phosphoric acid and purine bases. Such a cleavage 

 can, on the contrary, be brought about by erepsin (NAKAYAMA) or by 

 other closely allied enzymes which have been called nudeases (!WANOFF, 

 FR. SACHS). Micro-organisms can also bring about a more or less deep 

 cleavage of the nucleic acids (SCHITTENHELM and ScHROTER 2 ). 



The animal nucleic acids, with the exception of guanylic acid and 

 inosinic acid, are very closely related to each other, although they are 

 not identical. They all yield thymine as a cleavage product ; and as the 

 most studied representative are the nucleic acids of the thymus gland 

 (thymus nucleic acids) it is advisable for the present to treat them as 

 one group, which has received the common name of thymo-nucleic acids. 



Thymonucleic Acids. The most important investigations on the 

 nucleic acids have been carried out by KOSSEL and his collaborators, 



by MlESCHER, SCHMIEDEBERG, STEUDEL, LEVENE, and LEVENE and 



MANDEL. S A. NEUMANN has isolated two nucleic acids, a- and ^-thymus 



1 Proc. Roy. Soc., 72. 



2 Nakayama, Zeitschr. f. physiol. Chem., 41; Iwanoff, ibid., 39; Fr. Sachs, " 1st die 

 Nuklease mit dern Trypsin identisch?" Inaug.-Dissert, Heidelberg, 1905; Schitten- 

 helm and Schroter, f. physiol. Zeitschr. Chem., 41. 



3 The work of Kossel and his pupils on the nucleic acids can be found in: Arch, 

 f. (Anat. u.) Physiol, 1892, 1893; Sitz. Ber. d. Berl. Akad. d. Wiss., 18, 1894; Centralbl. 

 f. d. med. Wiss. 1893; Ber. d. d. chem. Gesellsch., 20 and 27; Zeitschr. f. physiol. 

 Chem., 22 and 38; see also Neumann, Arch. f. (Anat. u.) Physiol., 1898 and 1899 

 Suppl.; Miescher, Hoppe-Seyler's Med. chem. Unters., p. 441 and Arch. f. exp. Path, 

 u. Pharm., 37; Schmeideberg, ibid., 37, 43, and 57; Altman, Arch. f. (Anat. u.) 

 Physiol., 1889; Ascoli, Zeitschr. f. physiol. Chem., 28 and 31; Levene, ibid., 32, 37, 

 38, 39, 43, 45; Levene and Mandel, ibid., 46, 47, 49, 50; Inouye and Kotake, ibid., 

 46; Steudel, ibid., 42, 43, 46, 49, 50, 52, 53, 55, 56. 



