636 STUDIES IN GENERAL PHYSIOLOGY 
might say the change in the character of the contact causes 
an increase in the cell-divisions. This is still more obvious 
where whole organs are produced or regenerated. In one of 
my former papers I pointed out a very definite chemical dif- 
ference between embryonic tissue and muscle tissue.’ The 
former is more immune against K ions and more sensitive 
toward Ca ions. It has long been noticed, especially by 
botanists, that young tissue contains comparatively more K 
than old tissue. I am inclined to assume that this accounts 
for the fact that young tissue contains more water or has a 
greater degree of turgidity than old tissue. An increase in 
K allows the protoplasm to take up more water, an increase 
in Ca has the opposite effect.’ Ion effects and the effects of 
certain enzymes of liquefaction or solidification are often 
similar, or may at least support each other. It is not impos- 
sible that the increase in cell-divisions among the cells of 
the margin of the wound may be due to the different charac- 
ter of the contact to which these cells are exposed during or 
after the lesion, inasmuch as this different contact sets free 
or throws into activity certain enzymes which do not act as 
long as these cells are in their natural surroundings, e. g., as 
long as they are in contact with other cells. 
In returning after this digression to our main subject we 
must mention that the nature of the contact is not the only 
means by which solid elements in living tissues may be 
liquefied. Five years ago I proved that lack of oxygen 
liquefies the cell walls in the blastomeres of a teleost egg 
(Ctenolabrus),’ and Budgett showed in my laboratory that 
lack of oxygen produces the same phenomenon in Infusoria.' 
This case may find its explanation through the well-known 
experiment of Pasteur on the effect of oxygen on yeast cells. 
With plenty of oxygen the yeast cells multiply abundantly, 
1 Part II, p. 559. 2 Part IT, p. 510. 3 Part I, p. 370. 
4BupeGeErt, American Journal of Physiology, Vol. I (1898), p. 210. 
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