408 CHEMISTRY OF THE PROTEIDS CHAP. 



but otherwise they differ in their composition. They contain no 

 carbohydrate; on digestion with pepsin and hydrochloric acid they 

 yield a pseudo-nuclein ; the pseudo-nuclein of the synovial nucleo- 

 albumin amounts to about 4 per cent of the albumin, and contains 5 

 per cent of phosphorus. 



VII. HISTONE 



Histones are albuminous substances which, possessing a relatively 

 high percentage of basic radicals, are therefore preponderatingly 

 basic. 1 For this reason they are precipitated by alkalies which 

 constitutes their most remarkable property, although most histones 

 redissolve on adding an excess of alkali. They are very soluble in 

 acids, and therefore are in every respect the opposite of such acid- 

 albumins as the globulins and caseinogens. Histones do not occur in 

 the free state, but always coupled with what Kossel calls a ' prosthetic 

 group.' Histones in such combinations give rise to some of the most 

 important cell -constituents known, namely, to haemoglobin, nucleo- 

 proteids, etc. 



The first histone was isolated by Kossel 2 from the red blood- 

 corpuscles of the goose. Another histone was extracted by Lilienfeld 

 from the leucocytes of the thymus ; and to this group belong also 

 certain albumins occurring in combination with nucleic acid in the 

 spermatozoa of fishes. Finally, the albuminous radical of haemoglobin, 

 namely, the 'globin/ is also held to be a histone, although it differs 

 somewhat in its reactions from the other histones. Globin contains 

 less arginin than a typical histone, but, on the other hand, it contains 

 a higher percentage of histidin than does any other albumin. 



Bang 3 gives five reactions as typical of histones (see below) ; but 

 it is necessary to point out that the distinctly basic character of the 

 histones is of more importance than is the presence or the absence of 

 some of these reactions, which are not common to all the members of 

 the histone-group. Attention must also be drawn to the fact that, 

 as in the case of the globulins so here, the acid-albumin radical of any 

 given albumin has occasionally been mistaken for a histone, for in 

 acid-albumins the albumin plays the part of a base. 



1 A. Kossel, Deutsche med. Wochenschr. 1894, p. 146 ; Ber. d. deutsch. chem. Oes. 

 34. III. 3214 (1901) ; Bull, de la Soc. chim. de Paris, 3rd ser. vol. xxix. No. 14, 

 July 20, 1903 ; A. Kossel and F. Kutscher, Zeitschr. f. physiol. Chem. 31. 165 

 (1900). 



2 A. Kossel, ibid. Q. 511 (1884). 



3 J. Bang ibid. 27. 463 (1897). 



