he
stimulating of carbohydrate-splitting enzymes, which increases the supply
of easily oxidizable simple carbohydrates, thereby tending to compensate
for the decrease in respiratory activity. Further, increase in acidity
increases proteolysis, thereby liberating alkaline ammonia-derivatives
which tend to neutralize the rising acidity and so to restore normal
neutrality or alkalinity. Thus it will be seen that in the very great
sensitivity of its enzyme catalysts to slight changes in the reaction of
the medium, the protoplasm possesses a very efficient mechanism for
regulating changes and restoring equilibrium, if the latter be disturbed by
any abnormal conditions. It should also be noted, at this point, that the
almost universal presence in protoplasm of salts of carbonic and phosphoric
acids acts as an additional "buffer" against pronounced changes in reaction
of the material; the bicarbonates acting by means of their ready release or
absorption of carbon dioxide, and the phosphates by their easy change from
mono-sodium phosphate to di-sodium phosphate, and _vice versa_, the former
being slightly acid and the latter slightly alkaline in reaction.

A third effect of increasing acidity is that it induces increased
imbibition of water by the colloidal gel and causes swelling of the tissue.
After death, when the reaction of the protoplasm becomes pronouncedly acid,
this swelling often proceeds to the point of rupturing of the cell-wall, or
internal membranes of the protoplasm, thus permitting the entrance of the
putrefactive bacteria and hastening the decay of the tissue.

Finally, comparatively slight variations in the reaction of the protoplasm
produce enormous changes in its colloidal condition, affecting in a very
marked degree its permeability, its power of adsorption, etc.

It is clear, therefore, that variations in the chemical reaction of
protoplasm profoundly affect its colloidal condition, its enzymic activity,
and its respiratory processes. This necessarily brief survey is sufficient
to indicate how important to the activity of the protoplasm is the chemical
reaction of the material, and the mechanism with which it is provided for
maintaining the favorable condition of neutrality or slight alkalinity.

SUMMARY

It is evident that, within the limits of a single chapter, it has been
possible to give only a very brief and incomplete discussion of some of the
most important app