ly used a knife for cutting a lemon. But, curiously,
this stain is so very like blood that the naked eye of even the most
skilful medical jurist would be deceived by it.

[Illustration: FOOTPRINTS.--(1) WHEN RUNNING. (2) STANDING. (3) WALKING.]

Footprints are usually left to the police to interpret. But, very
probably, the result is often a miscarriage of justice. When the police
are working up a case they would not be human if they did not view
evidence with a certain amount of bias. The scientific witness, on the
other hand, has no personal interest one way or the other. And,
moreover, the comparison of a naked foot with its supposed print on the
ground, or the fitting of a boot to a boot-mark, is a process requiring
not only the most exact measurements, but consideration of the kind of
mark made on different kinds of soil, and in the various positions taken
by the foot in standing, walking, and running. In running we press
mainly on the toes, and in walking the greater part of the foot comes
down, and the longer the foot rests on the ground the deeper is the
impress. In fact, an expert can make a pretty shrewd guess as to the
rate at which the owner of the foot was travelling, by considering the
size and depth of the footprint.

In order to make a comparison a cast has to be taken, if the mark is on
soft ground. This is done by heating the footprint with a hot iron, and
filling it in with paraffin. From this a plaster cast is taken, and it
can be preserved for comparison until someone is arrested.

When the footprint is found in snow, gelatine is used to take the form
of it, and from this also a plaster cast is made.

Of course, these operations have to be carried out with the greatest
care, for footprints are frequently the strongest pillars of an
indictment. In order to compare the foot of the suspected person, he is
made to walk, stand, and run, over a surface similar to that on which
the incriminating print has been found. There is one case in which the
scientific detective is certain--when the person has stood still on
soft, but firm and tenacious, soil.

The footprints represented in our sketch are those of course of naked
feet, which give the clearest impression. But a corresponding variation
occurs in all footprints made by persons wearing boots, so that the
attitude or action of the wearer is easily told.

Now and again some deformity, such as the possession of six or of only
four toes, leaves no roo