"We conclude, therefore, both from analogy and from direct
experiment, that the observed action on these organisms is not
dependent on light _per se_, but that the presence of free oxygen
is necessary; light and oxygen together accomplishing what neither
can do alone: and the inference seems irresistible that the effect
produced is a gradual oxidation of the constituent protoplasm of
these organisms, and that, in this respect, protoplasm, although
living, is not exempt from laws which appear to govern the
relations of light and oxygen to forms of matter less highly
endowed. A force which is indirectly absolutely essential to life
as we know it, and matter in the absence of which life has not yet
been proved to exist, here unite for its destruction."
What is the obvious implication? If oxygen in presence of light destroys
one of these minutest portions of protoplasm, what will be its effect on
a larger portion of protoplasm? It will work an effect on the surface
instead of on the whole mass. Not like the minutest mass made inert all
through, the larger mass will be made inert only on its outside; and,
indeed, the like will happen with the minutest mass if the light or the
oxygen is very small in quantity. Hence there will result an envelope of
changed matter, inclosing and protecting the unchanged protoplasm--there
will result a rudimentary cell-wall.