[macallum] cellular OSMOSIS AND HEREDITY 159 



with clilorides and yet not a trace of chlorides have 1 ever found in the 

 heads. 



It is manifest then that the nucleus actively excludes inorganic 

 salts and tJie question is how is it done. The answer is tliat the nuclear 

 membrane is so constituted as to exclude them and the only structure 

 so ooncemed is the nuclear membrane. 



This impemieability of the nuclear membrane has in some oases 

 been noted by others. Hamburger^ found that when the intestinal 

 epithelial cells are bathed witli different concentrations of sodium 

 chloride the cytoplasm is readily permeable to the salt, but the nucleus 

 manifests little or no pemieabiliity. Tliis, he found to be tiiie also of 

 the nuclei of the ciliated epithelial cells of the trachea, and of the 

 nuclei of the epithelial cells of the bladder. 



The absence of certain other compounds and these of the organic 

 kind must he specially noted. Except in rare cases, all pathological, 

 no fats are demonstrated in the nucleus even with the most sensitive 

 nmcrochemical reagents for fat, Kke scarlet red or sudan III. Further, 

 intranuclear glycogen has never been observed in the normal cell and that 

 of itself would postulate the absence of free sugar in the nucleus. We 

 know also that free sugar has never been found microchemically in the 

 nucleus. It is not quite certain but it seems probable from observations 

 on the point that the nucleus does not contain free proteins, like globu- 

 lins and albumins- 



The total exclusion, not only of inorganic salits, but also of fats and 

 free carbohydrates from the nucleus and the probable absence of free 

 pnotedns, is a fact of prime importance and it throws a new light on the 

 relation of the nucleus to the cytoplasm. 



What is found in the nucleus is chiefly an iron-holding nucleo- 

 protein which the histologist calls chromatin and which differs in 

 different kinds of cells, that of the pancreatic nuclei being somewhat 

 unlike in character thaA of the hepatic nuclei and this again differemfc 

 from the nucleoprotein isolable from the nuclei of renal cells, although 

 all are like one another in the main in their composition. These, iron- 

 holding nucleoproteins lare synthesized in the cytoplasm. Iwanoff * 

 found that the zymase from yeast cells synthesized phosphoric acid and 

 sugar and formed a compound in which the sugar was masked and which 

 did not give a reaction for phosphoric acid until it had undergone treat- 

 ment for SiOme time with strong nitric acid. This points strongly to the 

 probability that the synthesis results in the formation of the skeleton 



* Osmotische Druck. und lonenlehre, Vol. 3, pp. 2 and 57. 



»Zeit. fur Physiol. Chem.. Vol. 50, p. 281, 1907. /l\0'^C/O"N. 



