BISTIDIN. 443 



CjHjjNjOj . The analytical results correspond about as closely with 

 the theoretical percentages required for this formula as with CgHgNjO,.' 

 According to this interpretation of histidin, like arginin, it should 

 yield on cleavage urea, guanidin and d amido valerianic acid. The 

 latter has been repeatedly found among the cleavage products of the 

 protamins.^ The conversion of creatin into creatinin is analogous to 

 that shown above with the difference however that water and not 

 ammonia is given off. 



If the above view of the origin of histidin be correct it will be 

 seen that the hexon bases acquire a new importance in so far as they 

 would form antecedents of the pyrimidin and even purin bodies. 

 The nucleus of the cell therefore would transform the ready-made 

 protoplasmic bases into the characteristic nuclein bases. 



Histidin itself forms well defined rhombic plates or needles. It 

 is not very soluble in water and hence can be crystallized from it 

 direct or by addition of alcohol. The solution shows faint alkaline 

 reaction and does not take up carbonic acid (Hedin). It is insoluble 

 in alcohol and in ether. According to Kossel,' the free base is levo- 

 while its salts are dextro-rotatory ; and the rotation is increased by 

 the presence of free acid. Histidin from thymus histon, according 

 to Lawrow/ is dextro-rotatory, which fact considered in connection 

 with the difference observed between the chlorid of histidin from 

 histon and from other sources, may be taken to indicate different 

 histidins. 



The free base is usually obtained from the chlorid by decomposi- 

 tion with silver sulphate. Possibly histidin unites with either of 

 the other hexon bases. This is indicated in the isolation of a com- 

 pound, CjgHjjNyOj, by Kossel and Mathews,^ from sturin by diges- 

 tion with trypsin. This compound consists probably of one mole- 

 cule of histidin and two molecules of lysin. Sturin itself probably 

 contains the three bases in combination. 



The monochlorid," CjHgNjOj.HCl + Hp, is obtained on decom- 

 position of the histidin-silver compound with hydrochloric acid 

 (Hedin) and crystallizes in fine, large, glassy plates which do not lose 

 water of crystallization at 120°, but do at 135° (Hedin), at 105° 

 (Kossel). It melts at 251°- 252°; is easily soluble in water, in- 

 soluble in alcohol and in ether. The aqueous solution is acid in re- 

 action and is slightly dextro-rotatory, although Hedin first consid- 

 ered it to be inactive. The chlorid from gelatin and from silk melts 

 at 243° (Wetzel). 



The di-chlorid,' C,HgN302.2HCl, contains no water of crystalliza- 



^Zeits. phyml. Chem., 22, 184, 194. 



'Zeits. physiol. Chem., 26, 590 ; 31. 



'Zeits. physiol. Chem., 28, 382. 



* Zeits. physiol. Chem., 28, 392; 31, 193. 



^Zeits. physiol. Chem., 25, 193 ; 31, 185. 



^Zeits. physiol. Chem., 22, 182, 192; 25, 192; 28, 387, 460. 



■<Zeits. physiol. Chem., 28, 383, 392; 31, 189, 193. 



