ation of a dual nature will a person become a thief or a
murderer unless there is really in that person a latent tendency towards
stealing or killing. There is always some germ of Mr. Hyde's
bloodthirstiness in the benevolence of Dr. Jekyll.

But Penelope Wells, under the domination of her Fauvette personality,
now entered upon a course that was certain to bring disgrace and sorrow
upon a man she loved with all her heart, a man for whom she had risked
her life on the battle field. Here is one of those mysteries that will
not be cleared up until we better understand these strange and
distressing phenomena of the sick brain or the sick soul.

In presenting this development it must be mentioned that Dr. William
Owen was not only a specialist on nervous diseases but a chemist of wide
reputation in the field of laboratory investigation. For a year and a
half preceding the end of the war he had held a major's commission in
the army and had spent much time in a government research laboratory,
studying poison gases.

In August, 1918, he had discovered a toxic product of extraordinary
virulence, not a gas, but a tasteless and odorless liquid containing
harmful bacteria. These bacteria showed great resistance against heat
and cold and were able to propagate and disseminate themselves with
incredible rapidity through living creatures, rats, earth worms, birds,
cattle, dogs, fleas, that might feed upon them or come in contact with
them. The deadliness of this product was so great, as appeared from
laboratory tests, that it was believed all human life might be
exterminated in a region intensively inoculated (from airplanes or guns)
with the liquid. This was only a possibility, but it was an enormously
important possibility.

A report on this formidable discovery had been prepared by Dr. Owen for
the Washington authorities with such extreme secrecy that the chemical
formula for the liquid had been indicated simply by the letters X K C,
the product being referred to as X K C liquid. Moreover, the only
person, except Dr. Owen, in possession of the full facts touching this
discovery was Captain Herrick who had assisted the doctor in his
investigations. Herrick had been cautioned to guard this secret as he
would his life, since there was involved in it nothing less than the
possibility of preventing future wars through the power of its potential
terribleness.

The bearing of all this upon our narrative was presently made clear as
t