Neoplastic Growths 269 



It is evident that work in this field is particularly difficult, because 

 the interpretation ol the results depends on the action of two agents, 

 each having a (oniplex nature. It has recently been shown that nieta- 

 jihase chromosomes could be singled out and destroyed in a beam of 

 neutrons^'' Modern cytological and radiobiological methods should 

 enable similar experiments to be jjerformcd with arrested metaphases. 

 1 he exploded type would be an excellent test object for a study of 

 the action of irradiation on isolated chromosomes. 



10.8: The Study of Carcinogenesis 



Chapter 9 has shown how useful colchicine could be in the analysis 

 of growth. It is regrettable that more studies have not been done 

 on the first stages of malignant change under the effect of various 

 carcinogens. For instance, the action of azo-dyes on the liver, and the 

 various factors which are known to influence the origin of liver car- 

 cinomas have never been subjected to the colchicine method. From 

 the few instances which will be quoted here, there is little doubt that 

 the early changes in mitotic activity in the liver would be fascinating 

 to study with the colchicine tool. 



In one of the first modern papers on colchicine, this was de- 

 scribed as a tool for the detection of the increased mitotic rate in 

 the skin of animals painted with the methylcholanthrene.-^ Shortly 

 after, in the 39th Annual Report of the Imperial Cancer Research 

 Fund, similar findings were described in mice painted with benzo- 

 pyrene. This British work does not appear to have ever been pub- 

 lished in extenso. These early results, demonstrating for the first 

 time that mitotic activity is increased shortly after the application of 

 carcinogens, is in agreement with later findings." These confirm the 

 idea that some subtle cellular change takes place soon after the first 

 painting with a carcinogen even when no malignant growth will 

 develop for several weeks. Colchicine could evidently be used for 

 studying all the intermediate stages between benignancy and cancer- 

 ous growth. 



Another observation published in 1934 is remarkable.-^ In methyl- 

 cholanthrene-treated mice a great increase in the numbers of mitoses, 

 as detected by colchicine, was found in the thyroid, in the salivary 

 glands, and in histiocytes. The meaning of this remains unknown. 



A single paper gives a detailed cytological study of the hair follicles 

 of mice,^4 [^ normal skin, in embryos, and in skin painted Avith 

 methylcholanthrene. Ultracentrifugation studies were carried out to 

 study the cellular viscosity. This was not found to be modified, even 

 in arrested mitoses. 



rhere is also a possiljihty that colchicine may act as an anti- 

 carcinogen. In mice im]jlanted with methylcholanthrene and in- 



