332 



CELL-CHEMISTRY AND CELL-PHYSIOLOGY 



albumins, which are compounds of pseudo-nucleinic acid with albumin 

 and yield no nuclein-bases (xanthin, hypoxanthin, adenin, guanin) as 

 decomposition products. 



The distribution of these substances through the cell varies 

 greatly not only in different cells, but at different periods in the life 

 of the same cell. The cardinal fact always, however, remains, that 

 there is a definite and constant contrast between nucleus and cytoplasm. 

 The latter always contains large quantities of nucleo-albumins, certain 

 globulins, and sometimes small quantities of albumins and peptones ; 

 the former contains, in addition to these, nuclein and nucleo-proteids, 

 which form its main bulk, and its most constant and characteristic 

 feature. It is the remarkable substance, nuclein, which is almost 

 certainly identical with chromatin, that chiefly claims our attention 

 here on account of the physiological role of the nucleus. 



2. The Nuclein Series 



Nuclein was first isolated and named by Miescher, in 1871, by 

 subjecting cells to artificial gastric digestion. The cytoplasm is thus 

 digested, leaving only the nuclei ; and in some cases, for instance pus- 

 cells and spermatozoa, it is possible by this method to procure large 

 quantities of nuclear substance for accurate quantitative analysis. 

 The results of analysis show it to be a complex albuminoid substance, 

 rich in phosphorus, for which Miescher gave the chemical formula 

 Qo^gNgiy^- The earlier analysis of this substance gave some- 

 what discordant results, as appears in the following table of per- 

 centage-compositions : 1 



These differences led to the opinion, first expressed by Hoppe- 

 Seyler, and confirmed by later investigations, that there are several 

 varieties of nuclein which form a group having certain characters 

 in common. Altmann ('89) opened the way to an understanding of 

 the matter by showing that "nuclein " may be split up into two sub- 

 stances ; namely, (i) an organic acid rich in phosphorus, to which he 



1 From Halliburton, '91, p. 203. [The oxygen-percentage is omitted in this table.] 



