DETAILS OF MITOSIS 



97 



4. Pathological Mitoses 



Under certain circumstances the delicate mechanism of cell-division 

 may become deranged, and so give rise to various forms of patho- 

 logical mitoses. Such a miscarriage may be artificially produced, as 

 Hertwig, Galeotti, and others have shown, by treating the dividing 

 cells with poisons and other chemical substances (quinine, chloral, 

 nicotine, potassic iodide, etc.). Pathological mitoses may, however, 



C D 



Fig. 45. — Mitosis in Actinosphcerium. [R. Hertwig.] 

 A. Encysted form, with resting nucleus; chromatin aggregated into large nucleolus-like body. 

 B, prophase of division of the encysted form, showing chromosome-like bodies formed of granules, 

 and spindle without centrosomes. C. Earlier prophase of the first maturation division, sliovving 

 extrusion of chromatic substance to form the centrosome. D. Later stage, showing centrosome 

 and aster. 



occur without discoverable external cause ; and it is a very interesting 

 fact, as Klebs, Hanscmann, and Galeotti have especially pointed out, 

 that they are of frequent occurrence in abnormal growths such as 

 cancers and tumours. 



The abnormal forms of mitoses arc arranged by Hansemann in two 

 general groups, as follows: (i) asymmetrical mitoses, in which the 

 chromosomes are unequally distributed to the daughter-cells, and (2) 

 nuiltipolar mitoses, in which the number of centrosomes is more than 



