DETAILS OF MITOSIS 



97 



4. PatJiological 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 treatins; the dividing- 

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

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



B 



C 



D 



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



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

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

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

 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, Hansemann, 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 are 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) 

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



H 



