PROLIFERATIVE DISEASES 



cells to grow and multiply, rather than of stimulating cells to 

 abnormal activity. This is based, perhaps rather inadequately, 

 on the behaviour of cells in tissue culture and in the process 

 of repair, plus, perhaps, the feeling that control of any sort 

 of mechanism tends to take the form of inhibitory devices. 

 We assume that in the body the internal environment con- 

 tains adequate nutrients to allow any cell to grow like a 

 malignant cell, but that each cell is prevented from so doing 

 by a variety of intrinsic and extrinsic controls. 



In Addison's disease and in experimental adrenalectomy, 

 there is a moderate enlargement of lymph nodes and a blood 

 lymphocytosis — the obvious implication is that adrenal hor- 

 mones play a part in the control of lymphocyte levels in the 

 body. It is well-known that in acute lymphatic leukaemia in 

 children there is a well-marked response to the administra- 

 tion of cortisone, indicating that, to some extent at least, the 

 cells concerned are still responsive to that particular control. 

 The other controls of the lymphocyte, both as regards 

 numbers in the peripheral blood and the total number and 

 distribution within the body, are still unspecified. There is 

 a very interesting hint from the work of my colleague 

 Metcalf (1956), that the thymus secretes a lymphocytosis- 

 stimulating factor which may play a part in the hormonal 

 control of levels of lymphocytes in the circulating blood. 



3. Experimental leukaemia 



Most of the recent work on experimental leukaemia has been 

 concerned with the spontaneous disease as seen in pure 

 strains of mice. This work has been important in defining 

 some of the hormonal controls which can prevent or accelerate 

 the appearance of leukaemia, and, before continuing the 

 discussion of human leukaemia, it seems desirable to provide 

 a short account of the experimental studies in mice. Follow- 

 ing largely the work of Hauschka, Furth, Kaplan and Law 

 (as reviewed in Hauschka and Furth, 1957; Law, 1957; 

 Kaplan, 1954), we may summarize the features of mouse 



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