160 ROYAL SOCIETY OF CAxNADA 



of tlie nucleic acid molitule. As the yeast cell has no nucleus, and as tlie 

 zymase is a fennent or rather several fennents, it is very probable that 

 nucleic add is formed in the cytoplasm of the various cells of the body. 

 The neucleic acid once formed readily combines with protein and then 

 the nucleoprotein diffuses out of the cell where it is synthesized, or into 

 the adjacent nucleus where it is stored. Those wliich diffuse out may 

 I each the interior of other nuclei or the nuclei of other species of cells. 



The nuclear membrane is permeable to such iron-holding nucleo- 

 proteins. The diffusion outwards from the nucleus of the developing 

 nerve cell of all or nearly all its chromatin to constitute the material 

 of the Nissl granules has been already referred to. The presence of 

 prozymogen in the cytoplasm of secreting cells, such as those of the 

 salivary, gastric, and pancreatic glands is duo to a chromatin-like com- 

 pound diffusing from their nuclei. 



It is highly probable that the permeability of the nuclear membrane 

 by the iron-holding nucleoproteins is due to a degree of solubility of 

 the latter in the subetance of the membrane, just as copper oleatc is 

 soluble in the membrane of Kahlenberg's experiments. Why the iron- 

 holding nucleoproteins gather in the nucleus in such a quantity as we 

 find there and do not diffuse out again is easily susceptible of an explana- 

 tion. It probably passes through the membrane to the nuclear cavity in 

 the water-solid phase, that is, in the hydrophilous form, but in the nuclear 

 pavity it enters into the other condition, namely, the solid-water phase 

 in which there is more solid and less water, and consequently, it is much 

 less diffusible and more inert. 'There can be no doubt that the less 

 diffusible phase does occur inside the nucleus, for it constitutes the 

 chromatin loops so familiar to the cytologist and histologist. What 

 (transforms the one phase into the other can at present be only a matter 

 of speculation as y«t, but it may be suggested that the nuclear mem- 

 brane brings about I this change for the chromation in not a few species 

 of nuclei lines the inner face of the nuclear membrane, indicating that 

 the transformation occurs in the membrane or in, its immediate vicinit}'. 



The nuclear membrane being permeable only or chiefly to iron- 

 holding nucleoproteins, several conclusions follow. One that iron-holding 

 nucleoproteins so long as they remain in the interior of the nucleus are 

 protected' from chemical alteration due to the action of inorganic and 

 •other compounds which may invade the cytoplasm. Another is that this 

 is the true function of the nucleus. 



These two conclusions based on the composition and the properties 

 of the nuclear membranes enable us to comprehend dearly what con- 

 stitutes the physdoal basis of heredity. 



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