Experimenfal Growth in Animals 223 



These studies of the epithelial growth in mice lead to a most 

 interesting development which will now be considered: the study of 

 groAvth in cxplantcd tissues. 



y.5-2; Grou'tJi in vitro. Many of the fundamental discoveries 

 related to colchicine-mitosis were made on tissue cultures.^- -^' '^^- '''-• 

 84, 88, 90 ^hc importance of metaphase arrest in increasing the num- 

 ber of visible mitoses without modifying the mitotic rate has been 

 illustrated bv Figme 9.1. Other results on the action of colchicine on 

 neoplastic cells in tissue culture, and on the mitosis-arresting proper- 

 ties of colchicine derivatives and other mitotic poisons will be related 

 in Chapters 10 and 17. Tissue culture work offers definite potentiali- 

 ties for further investigation. The utilization of synthetic or semi- 

 svnthetic media and the roller-tube technique are some of the modern 

 aspects of tissue culture Avhich could benefit from colchicine. 



On the other hand, most important results have been obtained 

 by simplified methods in which surviving tissues are utilized. Within 

 the short duration of the experiments, mitoses proceed normally, and 

 problems of bacterial contamination, transplantation, and dediffer- 

 entiation do not arise. These methods have been used in the study 

 of the skin and bone marrow of mammals, including man. 



As a consequence of previously mentioned work on the skin of 

 the ears of mice, Bullough-^ developed a technique of in vitro study 

 of the mitotic activity. In vivo experiments had demonstrated that 

 glucose-*' and oxygen-' were indispensable for providing the energy 

 required for cell di\'ision. Glutamate was further demonstrated to 

 increase the rate of cell division. The /?? vitro method should eventu- 

 ally bring forth important new data on the metabolic requirement 

 of epidermal cells. Colchicine increases the amount of visible mitoses 

 and makes counts simpler. However, because of the long duration 

 of cell division in this type of tissue, colchicine does not produce any 

 of the spectacular increases \\'hich have been seen in other organs. 

 An important residt was to establish that a linear relation existed 

 between the number of arrested mitoses and the oxygen tension. 

 While only 0.4 mitoses could be seen in pure nitrogen, the figures 

 were 3.9 for 60 per cent nitrogen and 40 per cent oxygen, and 8.3 in 

 pure oxygen.-" The general significance of these results is made clear 

 bv nearly identical findings with bone marrow cells.'' This work has 

 been done mainly in Ital)'. Astaldi and a group of collaborators first 

 studied the colchicine response of human bone marrow.*' This is 

 readily available by sternal puncture, and colchicine has provided 

 a new insight on the growth of this tissue. This growth is far more 

 rapid than that of skin; in mammals, bone marrow and intestinal 

 mucosa are the tissues which ha\e the highest mitotic index. After 

 explantation, small fragments were kept at 37°C. in human serum, 



