and whatever the motive for this work, we know that mustard gas
must have received the early attention of the German War Office,
for it was approved and in production early in 1917.
Although the Medecin aide-major Chevalier of the French services
drew attention to its importance in 1916, the French had no serious
thought of using mustard gas, and did not realise its possibilities
until the German battle experiment of July, 1917. It is not
generally known, however, that other vesicant compounds were employed,
notably some of the arsenic compounds, and the Germans were researching
on substances of this nature which gave great promise of success.
Mustard gas provides a striking example of the organic way
in which chemical warfare is bound up with the dye industry.
The compounds required for its manufacture were those which had been
made on a large scale by the I.G. for the production of indigo.
World indigo monopoly meant possession of a potential mustard gas
surprise on the outbreak of war.

Sneezing or Sternutatory Substances.--The last class,
the sternutatory substances, produced the familiar sneezing
effect which was accompanied by intense pain and irritation
of the nose, throat, and respiratory channels. They were mostly
arsenic compounds and were not only sternutatory but also toxic,
producing the after effects of arsenic poisoning.

The Tactical Classification.--From the point of view of our account
of chemical warfare, however, the physiological classification
of these substances is not so important as the tactical and,
indeed, once this grouping of the substances is understood,
a profound knowledge of their chemical nature is not necessary.