DEDIFFERENTIATION IN PEROPHORA 671 
‘his is particularly well seen in malignant tumours, which 
will continue to grow at the expense of the rest of the body, 
even when this is in a condition of relative starvation. In 
tumours derived from adipose tissue, the tumour-cells may be 
full of fat after all vestige of fat has disappeared from the 
normal tissues. The fact that regeneration will proceed 
actively and normally in starving Planarians exemplifies the 
same state of affairs. 
We saw above that we should expect the reaction to proceed 
to a limit, all the product of the slower process bemg utilized 
by the faster. As a matter of fact this hmit can often not be 
reached, since life is not possible when the ‘ subordinate ’ region 
is absent, or else its reduction brings about subsidiary changes. 
It is also complicated by the supervening of dedifferentiation. 
That starvation can produce dedifferentiation has been shown by 
Schultz (1906), by Runnstrém (1917), &e. It therefore follows 
that the tissues of the less active region will usually, as a result 
of the starvation induced, reach a stage at which they are 
unable to maintain themselves, and will start to dedifferentiate. 
In the dedifferentiated state they will possess a still lower 
rate of metabolic activity, and so the resorption-process will 
be accentuated. 
Next we meet with the fact of differential susceptibility. 
This is a corollary of difference in rates of reaction. The more 
highly-differentiated region and system, or the one with 
higher metabolism, will be, ceteris paribus, more sus- 
ceptible to unfavourable conditions. If it is placed in a toxic 
solution, for instance, it will enter into reaction with more of 
it in a given time than will a slower system. There are a number 
of complicating factors (such as acclimatization) which enter 
into the problem, but, broadly speaking, we may say that 
a more highly-differentiated and more active system will 
be relatively more interfered with than a less highly-differen- 
tiated and less active system. 
After a certain point of interference is reached, dedifferentia- 
tion will set in. Dedifferentiaticn is the primitive reaction of 
organisms to unfavourable circumstances. More energy is 
wey 2 
