THE LAWS OF CELL MULTIPLICATION 269 



origin to the daughter cells, and it is the daughter cells 

 which attain full differentiation and form the specific 

 cells of the tissue. More rarely the functional cells 

 themselves by reversion to a more embryonal type can 

 take on the properties of mother cells. 



3. Under abnormal conditions, the fully differentiated function- 



ing cells of certain tissues are capable of proliferation and 

 giving rise to cells of like nature, but this is only after 

 a preliminary reversion to a simpler, more embryonic 

 type. The fully differentiated cell as such is incapable 

 of proliferation. 



4. Or, otherwise, the energy stored up by the cell may be 



expended in one of two directions, but not in both — 

 either in functional activity or in preparation for pro- 

 liferation ; and, the structure of a cell being the expression 

 of the activity of that cell, the expenditure of energy 

 in either direction is attended by corresponding mor- 

 phological or structural differences in the cell. 



5. The more highly differentiated a cell, the more highly 



elaborated its structure, the less the ease with which it 



reverts, and the less the liability to reversion to a simpler 



reproductive form ; the simpler the cell, the greater 



the ease and the greater the liability to such reversion. 



It is thus possible, at the one extreme, to conceive cells 



so simple in function and in structure that functional 



or reproductive activity may be called into play without 



recognizable preliminary structural alteration, and, at 



the other, cells so highly differentiated that the capacity 



for proliferation has become entirely lost. 



The law with its corollaries here given does not so far appear 



to have obtained general recognition. Certainly I fail to find it 



explicitly referred to by writers upon morbid anatomy, and had 



it been currently accepted by biologists it would ere this have 



become part and parcel of pathological teaching. It is only 



after some little search and almost by chance that I find its 



main paragraph laid down by Kolliker in 1885, and that only, 



as it were, in passing, in an article not dealing directly with 



regeneration, but dealing with the part played by the nucleus in 



inheritance. In that article Kolliker states : ' In all cases in 



which an organ or a tissue is capable of regenerating itself, it 



