﻿1903] NUCLEAR MEMBRANE 3 1 5 



various stages of mitosis. Immediately after the nucleus divides 



there are two masses of chromatin in the cell. For some time 



\ these masses of chromatin are surrounded by neither karyo- 



lymph or membrane, and yet no one will deny that they are 

 nuclei. The law that the nucleus never arises de iiovOy but 

 always from the division of a preexisting nucleus, does not hold 

 good if we regard the membrane, karyolymph, or nucleoli as 

 morphological elements. We must either change this law of 

 the permanency of the nucleus or change our morphological 

 conception of this organ. As there seems to be no doubt as to 

 the permanency of the chromatin from cell to cell, and as the 

 other constituents of the mature nucleus are physiological results 

 which are entirely renewed with each succeeding mitosis, there 

 is good reason to regard the chromatin alone as the nucleus, 

 whether it is surrounded by karyolymph and membrane or 

 lying freely in the cytoplasm. 



The question as to the existence of a nucleus in the Cyano- 

 phyceae and Bacteria has been the subject of controversy for a 

 great many years and even up to the present time it has not been 

 satisfactorily shown that such an organ exists in the cells of 

 these primitive organisms. Among the modern workers in this 

 field, as Zukal (1892), Palla (1894), Nadson (1895), Butchli 

 (1S92-1896), Zacharias (1897), Fischer (1897), and Macallum 

 (1895-1900), a great divergence of opinion is expressed. Some 

 claim that a nucleus is present; while on the other hand many 

 claim that no structure exists that can be interpreted as a 

 nucleus : others again have shown quite conclusively that chro- 

 matin-like granules are present, but hold that these do not rep- 

 resent the nucleus. Of the writers who hold this latter view 

 Macallum (1900) expresses himself probably more strongly than 

 the others. In his work ** On the cytology of non-nucleated 

 organisms" he finds that the cells of Beo:Qriatoa and of the Cyano- 



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phyceae contain granules which stain like chromatin and give all 

 its known reactions. Although he regards these structures 

 analogous to chromatin, he concludes that ** there is no nucleus 

 nor anj' structure which resembles a nucleus in the Cyanophy- 



He holds a similar view in regard to the Beggiatoa cell 



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