672 JULIAN 8. HUXLEY 
necessary to maintain a cell in a differentiated than in a dedif- 
ferentiated condition. This is especially clear when, as in 
most instances, differentiation involves an increase in the 
surface of the cell relative to its bulk; here the maintenance 
of differentiated form alone involves the expenditure of more 
energy. ‘Thus when the processes of life are interfered with 
by unfavourable agencies, the cell is unable to continue to 
produce the energy necessary for the maintenance of its 
differentiated state, and must either die or dedifferentiate. 
The main characteristics of dedifferentiation are the follow- 
ing : 
(a) Cells revert, if isolated to a spheroidal, if in epithelia to 
a cuboidal form. 
(b) Cytoplasmic differentiation is lost. 
(c) Organs containing cavities revert to simple spheroidal 
sacs. Junctions between organs are often broken. 
(d) Apertures usually disappear altogether. 
(c) The whole organism diminishes in size and reverts to 
a spheroidal form, owing to the form-changes in its constituent 
cells. This has the effect of increasing the opacity and density 
of the organism. 
Once dedifferentiation has started in any region or system 
the previous level of metabolic activity in that system is in- 
evitably much reduced. Thus, if dedifferentiation occurs in 
a dominant and not in a subordinate system, this dominant 
system will lose its dominance and become subordinate. 
Such alteration of equilibrium by unfavourable agencies we 
may call differential inhibition; it is a corollary of 
differential susceptibility. Differential inhibition need not, 
however, involve dedifferentiation, nor reversal of dominance. 
In a growing organism unfavourable agencies will depress the 
srowth of the domimant or more active regions relatively 
more than that of the rest, and we shall, as outlined above 
(p. 669), get a decrease in size of the former, an increase in the 
latter—a decrease and an increase which will be absolute as 
well as relative. This is illustrated in some of Child’s experi- 
ments (see later). 
