: IS IT ARSENIC, OR NOT?]

He knows that prussic acid kills like a bullet in the brain--a glass of
cold water taken while hot from exercise may do the same--and he smells
for it. He can also tell if it is phosphorus or carbolic acid, by the
smell.

He knows that relatives usually kill each other by means of particular
poisons; that other poisons are used for suicidal purposes; that the
photographer takes cyanide of potassium, the medical man and chemist
prussic acid or morphia, the poor man vermin-killer or oxalic acid, or
carbolic acid, or some such agonising destroyer of life. And thus,
though all poisons lead to the same end--stoppage of the breathing and
blood circulation--yet each has its own particular way of sending the
soul to eternity. He can therefore often tell the analyst detective how
to take a short cut.

[Illustration: THE SPECTROSCOPE--AN INSTRUMENT THAT HAS BEEN FATAL TO
MANY CRIMINALS.]

By the way, there is no such thing as a slow poison--that is, a poison
which, taken to-day, does not show its effects for weeks. This is a
fiction of the novelists. On the other hand, there is--except in the
case of prussic acid and nicotine--no death straight away after taking
poison, as one sees it on the stage, Shakespeare notwithstanding.

An actual case will show that the discovery of murder by the doctor and
analyst is not always plain sailing.

A good many years ago, a Mr. Sprague was tried for the murder of the
Walker family by means of the well-known poison of the deadly
nightshade. The medical evidence showed clearly that they all died from
belladonna poisoning, and belladonna was found in the rabbit-pie they
had for dinner. A common-sense jury, however, acquitted the prisoner;
and only recently have medical men solved the mystery by discovering
that rabbits can eat any quantity of this plant without suffering harm,
while their flesh becomes fatally poisonous.

A second case shows what wonders the chemists can work. A surgeon's wife
died from corrosive sublimate, given in a draught by her husband. He
said that, in making up the draught, he mistook a bottle of mixture,
which he had prepared for a sailor, for the water-bottle, and had poured
some of it into his wife's draught. The sailor's mixture was analysed,
and it certainly contained corrosive sublimate; but, not content with
finding the poison, the analyst measured the quantity present, and,
while the sailor's mixture contained only ten grains to a