INHERITANCE OF ACQUIREMENTS BY CELLS 301 



form, let me repeat, is not so much embryonic as proliferous. 

 It is peculiar to actively dividing cells at all times of life. 



Whatever the origin, therefore, of the tumour proper, however 

 it is started, what makes the tumour is the assumption by the primary 

 cells of that tumour of the habit of growth in place of the habit of 

 work, and, according to the extent of this replacement, so do we get 

 the various grades of tumour formation from the most benign to 

 the most malignant. 



SUMMARY OF ARGUMENT 



Let me now sum up the various points brought forward one 

 after another in arriving at this conclusion. They are : 



1. The katabolic activities of the cell are of two orders : 

 those determining the relationship of the cell with the exterior, 

 and those that are vegetative determining the continued existence 

 and multiplication of the cell ; the former excited by stimuli 

 of various orders from without, the latter only indirectly so 

 excited, being more directly called into play by conditions 

 obtaining within the cell. 



2. The controlling agency in at least the higher katabolic 

 activities of the cell, both "functional" and "vegetative," is 

 the nucleus, and nuclear activity is accompanied by break- 

 ing down and discharge, or by rearrangement of the nuclear 

 molecules. 



3. The changes which occur in the nucleus during the active 

 performance of the specific functions of the cell are of a character 

 so different from those observed during the process of cell division 

 that proliferation and active performance of specific function, 

 the one precluding the other, are obviously to a large extent 

 incompatible. The cell engaged in the active performance of 

 function in response to external stimulation cannot simultane- 

 ously proliferate. 



4. It follows, therefore, that active cell division and cell 

 proliferation occur only in conditions in which the cell cannot 

 fully utilize the assimilated material (and the energy stored up 

 in the assimilation of that material) in the performance of its 

 specific functions. 



5. Such conditions are to be met with where the tensions 

 acting on the cell are reduced and certain energies which before 



