only in very exceptional positions that compensa-
tions like those which we have just pointed out
could occur, and, without being able to indicate in
detail the results or the direction of the general resultant,
we see, nevertheless, that the total effect could not be
the same as in the first case. The path of the ray of
polarized light where the direction of the vibration
is constant and unique must depend on the direction
in which the obstacles it encounters are placed. With
out going into this problem further, it is possible to admit
that the deviation of the plane of polarization depends
on the manner of distribution of the obstacles, and that,
according as the dissymmetry in the atoms is right or
left there will be a right or a left rotation.

Of less importance is the mechanism of the action,
which always remains a little hypothetical. It is suffi-
cient that the experimental study of the tartrates has
linked indissolubly these two ideas: the molecular rotary
power, and the dissymmetry of the molecule. This
suffices to give us the right to attribute dissymmetrical
molecules to all substances acting in solution on polar-
ized light, and when one considers that all these sub-
stances belong to the vegetable or animal kingdom,
that is to say, are the products of cellular activity,
this peculiarity of structure becomes curious, if regarded
closely. Guided by an imagination at once so adven-
turous and so well controlled as was that of Pasteur,
we are constantly on the border of new countries, but we
journey with security.

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