THE MITOTIC CYCLE 



granules arise from the nucleoli of the secretory cells and are trans- 

 formed within the cytoplasm into spiral threads of mucus. 



Synthetic activity 



The thesis of Caspersson and his school that the nucleolus is a centre 

 of protein production, which we have discussed in a previous section of 

 this book (pp 13-17), like other recent developments in cell biology, is 

 thus a modern version of an older conception. It would be of great 

 interest to apply modern techniques to these extreme instances of 

 synthetic activity in which nucleoli are involved. Bradfield'^ has 

 studied the silk-glands and oocytes of the spider from this point of view; 

 the nucleoli of the latter are very large, they contain much ribonucleic 

 acid, and give a strongly positive phosphatase reaction. Balbiani'^^ in 



Figure 10 Y oun% oocyte o{ Limnae stagnalis 

 attached to wall of ovotestis. Material 

 from the nucleolus (N) is being extruded 

 into the cytoplasm (NP, NE). From 

 LuDFORD*' {By courtesy, J. Roy. micr. Sac). 



1864 observed movements in these same nucleoli, which continued for 

 some hours in a preparation of the living material under the microscope. 

 An amoeboid motion of the whole nucleolus was seen, together with 

 dilation of vacuoles within, which Balbiani compared with the action 

 of the Protozoan contractile vacuole. Movement of nucleolar vacuoles 

 was also observed by Bohm'^ in the oocyte o^Petromyzon. Again, a study 

 of the relationship of such movements to the synthetic activities of the 

 nucleolus might be of value. 



Changes in form of this body are not apparently confined to the 

 oocyte. Extrusion of nucleolar material into the cytoplasm of cells in 

 tissue culture has been described by Lewis''^ and by Ludford," who 

 observed the process in living material and did not regard it as ab- 

 normal. Strangeways'^ describes how the nucleoli repeatedly joined 

 together and separated when such cells were observed over a period of 

 several hours. Movements of the nucleoli of cells in culture is greatly 

 enhanced both when prophase approaches and during the first hour or 

 so of interphase. Sometimes vacuoles are seen in the nucleoli of both 

 normal and malignant cells (Lewis''^). Lasnitzki and Wilkinson^'' 

 have observed them in chick cells in culture treated with acridine 

 derivatives. Zollinger®^ has shown that when tissue cultures are 



40 



