378 Colchicine 



the physiology of cellular division in bone marrow and on the actions 

 of various substances on rate of cell multiplication (Chapter 9) . The 

 cells, which are suspended in homologous serum, are able to divide 

 regularly for more than 24 hours after explantation.- 



A method for iii vitro cultivation of immature rat ovaries has been 

 described" and should be of great interest for endocrinological re- 

 search. 



Colchicine has been used with the main techniques of tissue cul- 

 ture, especially with hanging-drop preparations, wdiich enable a con- 

 tinuous observation of growth. i- Some estimation of the quantitative 

 amount of newly formed cells may be made by planimetric measure- 

 ment of the whole culture, but the influence of cell migration must 

 not be neglected. 1- Tissue cultures are especially favorable for cine- 

 micrographic methods. i- A very thorough study of the action of col- 

 chicine on the rate of mitotic growth and on the repartition of the 

 various types of abnormal or arrested mitoses has been made possible 

 by this technique!-' ■>- (Chapter 9, Fig. 9.1). Tissue cultures are also 

 most useful for comparing normal and neoplastic cells,^! for the 

 study of synergists or antagonists of colchicine, and for testing other 

 mitotic poisons42 ^^f. Chapter 17) . It should, however, be mentioned 

 that cultures of chick fibroblasts will not always behave like fibro- 

 blasts from mammals.^^ For the study of colchicine derivatives or 

 other spindle poisons, cultures of various types of cells from different 

 animals should be compared. 



i6A.^-^: Mitotic counts. When colchicine is used as a tool for 

 studying growth (Chapters 9 and 10) , when the problem of mitotic 

 stimulation by colchicine is considered (Chapter 9) , or when sub- 

 stances acting synergically or as antagonists to the alkaloid are studied 

 (Chapter 17), a precise estimation of the number of mitoses in con- 

 trols and at various intervals after mitotic arrest is indispensable. 

 Some of the methods outlined in the preceding subsection provide 

 excellent material for counting cell divisions, but even with tissue 

 cultures, the problem may be complicated because only the periphery 

 of the explanted fragment grows rapidly. Precise counts of the total 

 number of cells in mitosis are possible both with the ear-clip tech- 

 nique^^' !■* and the methods of bone-marrow explantation.^ In more 

 complex tissues a reliable standard may be difficult to find. For in- 

 stance, many authors define the "mitotic index" as the number of 

 mitoses found in a given area, i.e., so many microscopic fields, of 

 tissue. This is a good method when dealing with uniform and fairly 

 simple tissues, for example, the regenerating liver,ii but not when 

 complex tissues are considered. In the small intestine of mammals, 

 for instance, it is preferable to count the number of mitoses per 



