HUMAN LEUKAEMIA 



and eosinophil leukaemia in which the cells present in 

 excessive numbers are much more mature than those in the 

 classical myeloid leukaemia (Scott, 1957). 



This raises a number of very interesting questions which, 

 if they could be answered, might do much to unravel the 

 process of differentiation amongst mesenchymal clones. If, 

 as all the evidence suggests, a single mesenchymal cell can, 

 under appropriate stimulation, give rise to clones which 

 contain both lymphocytic and granulocytic types, why does 

 a case of myeloid leukaemia consistently produce granulo- 

 cytic and not lymphoid cells and why in rare instances are 

 the dormant pathological cells almost mature leucocytes? 



'Somatic mutation' may well cover a wide variety of 

 processes and, as has been suggested, both for bacteria and for 

 Paramecium there may well be genetic mechanisms which can 

 be switched, as it were, from one functional phase to an 

 alternative one, the capacity to switch under appropriate 

 stimulus being itself under genetic control. On this view, 

 one of the common effects of somatic mutation to proliferative 

 over-activity is loss of the ability to switch to another physio- 

 logical type of activity. This is perhaps most strikingly seen 

 in the behaviour of multiple myelomatosis where the neo- 

 plastic clones are fixed in the plasma-cell condition. 



That this fixation is not invariable may perhaps be indi- 

 cated by the existence of such a syndrome as chronic 

 erythromyelosis, in which there is a blood picture with the 

 features of both polycythaemia and chronic myeloid leu- 

 kaemia with radiological evidence of medullary new-bone 

 formation. This speaks both for a unitarian view of mesen- 

 chymal cell origin and for the mutational change in these 

 cases having left more or less intact the capacity of cells of the 

 resultant clone to develop in various directions. 



{b) Chronic lymphatic leukaemia 



Chronic lymphatic leukaemia is a very different disease 

 from chronic myeloid leukaemia, for one thing in occurring 



12 177 BC 



