od, and
sixteen times as great in the blood of a fowl. Very important results
are expected from this principle.

Reliable as are the microscope and spectroscope, the analyst always uses
the third means at his disposal--the chemical test. For instance, he
gets a knife covered with dark red stains. Are they blood, or are they
only the rust formed by vinegar or the juice of a lemon that has
deceived so many people? Assuming that he has removed the stain, he
places the matter in any kind of tiny vessel, and drops in some tincture
of galls. If the thing is only rust, he has some excellent blue ink; if
it is blood, he finds that a reddish powder makes its appearance.

[Illustration: BURNING CLOTH IN THE LABORATORY.]

Perhaps he gets a handkerchief with a red stain. If the cloth is white
he can apply a test direct to it, but as a rule he prefers to dissolve
the stain out. Now, a handkerchief may be stained with a number of
different reddish things--Condy's fluid, jam, cochineal log-wood, or red
paint. He puts a drop of ordinary ammonia on the cloth. If the stain is
caused by currant, gooseberry, or other fruit juice it turns blue or
green; if it is Condy's fluid it becomes blue; if it is cochineal it
becomes crimson, and so on. But if it is blood, it does not change in
the least. Other tests might be described, but we have not the space.

Probably the most interesting of all his duties to the analyst is that
of judging from what animal the blood stains came. This can be done only
in some cases; that is, when the blood is not quite so old that the red
corpuscles have entirely lost their shape.

Of course this is a matter of the greatest importance when a man is on
his trial; for, in the first place, every spot of blood found on his
belongings is supposed to have come from his victim, although it may be
nothing more than the blood of a fish; and, in the second place, the
stock explanation of blood stains on his clothing offered by a prisoner
is that they came from some animal he killed. The plan is to ask him
what animal. Five times out of six he will say a domestic fowl or some
kind of bird especially if he is a poacher who has killed a
gamekeeper--and then he is done for.

Look at the pictures on page 149 and you have the whole thing in a
nutshell. It will be seen that the red corpuscles of the blood of birds,
reptiles, and fishes (with the exception of the cyclostomata) are oval,
while those of mammalian blood are round