STRUCTURAL DIFFERENTIATION OF THE NUCLEUS 



C. L. HUSKINS 



McGill University, Montreal 



From studies on protoplasm in general, presented by previous 

 speakers in this Symposium, we may proceed to a consideration of 

 the elaborate structural features which are present throughout the 

 life of the nucleus, even in the "resting" stage when many of them 

 are not directly observable. These are today being studied from 

 many different points of view and by very diverse techniques. To 

 simplify, and perhaps to promote, discussion we may classify these 

 attacks upon the problems of the nucleus into four groups, though 

 recognizing, of course, that there are many studies which overlap 

 the boundaries that are, rather arbitrarily, here laid down. Apart 

 from simplifying discussion, the classification may also serve a 

 useful purpose in emphasizing that some studies of the nucleus pro- 

 ceed in rather extraordinary isolation from others and that general- 

 izations made by workers of one group often ignore the data of the 

 other groups or, in soine cases, draw unwarranted conclusions from 

 them. The diversity in points of view and of detailed opinion found 

 among students of the nucleus indicate in themselves the complexity 

 of the structures within the boundary of the nuclear membrane and 

 the scope of the problems that remain to be elucidated. 



In the first of the four groups we may place all studies aiming at 

 the elucidation of the "submicroscopic" structure of the nucleus. 

 Often such investigations use wave lengths shorter than those of 

 visible light. The second level of analysis comprises all microscopic 

 studies with visible light of killed and fixed materials. The third 

 includes all the varied studies on the living cell made by the methods 

 of "experimental cytology." The fourth comprises the interpretation 

 of structure derived from observations of function made with the 

 techniques of genetics. 



Workers in any of these fields should, of course, be familiar with 

 all four. Unfortunately, few of us are! Accepting a more limited 

 standard, those working on the first level viust, of course, be familiar 

 with the data of the second group. The second group must today 

 know the techniques and discoveries of the geneticists if they are 



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