2l8 FINE-STRUCTURE OF PROTOPLASM II 



It is curious that of all these structures nothing is to be seen in the 

 electron microscope after optimal fixation with 4% neutral formalin 

 (RozsA and Wyckoff, 1950). It is true that the birefringent peri- 

 nuclear zone is only visible after fixation with OSO4, which according 

 to RozsA and Wyckoff produces artefacts. But in the polarizing 

 microscope the nuclear membrane appears equally after fixation with 

 4% neutral formalin, especially if its double refraction is enhanced by 

 4% sodium sulpho-antimoniate. From these facts it must be concluded 

 that there are oriented arrangements of amicroscopic molecules in the 

 nuclear boundary. Whether this structure should be called a "mem- 

 brane" is open to discussion. The actual evidence is rather in favour 

 of a phase boundary with the structure of a mesophase (Pischinger, 

 1950). 



The large nuclei of Amphibian oocytes seem to have a composite 

 nuclear membrane as revealed by the electron microscope (Callan, 

 Randall and Tomlin, 1949; Callan and Tomlin, 1950). A structure- 

 less sheet is covered by a layer with pores of 300 A diameter and 

 800 A distance in hexagonal array. This porous lamella serves as a 

 mechanical support of the homogeneous nuclear boundary, which must 

 have some amicroscopic structure since it shows semipermeability. 



Nuclear staining. The proteins isolated from the nucleus being 

 strong bases, it might be expected that it would be easy to dye the 

 structural elements. The living nucleus, however, can hardly be 

 stained without temporary or permanent damage (Becker, 1936). 

 For this reason it must be supposed that the basic groups which ionize 

 freely in the isolated protamines and histones are screened off in the 

 native state. If nevertheless one wishes to apply vital staining, these 

 groups must be liberated by slight hydrolysis. As in the case of cyto- 

 plasm, it can be said that vital staining, which means the formation 

 of coloured salts of the basic or acid dyestuffs applied, always repre- 

 sents a hydrolytic intervention; for instance, vital nuclear staining in 

 a dilute solution of erythrosin is only possible when acidified with 

 acetic acid. 



It is reasonable to assume that the basic protein groups are screened 

 by nucleic acids. Apparently, however, the active nucleus contains 

 this component rather sparingly, so that other anionic substances must 

 also take part in masking the basic groups. Active nuclei are less 

 intensively stained by the nucleal reaction than those which are 



