Columbia subject headings:
Gases, Asphyxiating and poisonous--War use.
World War, 1914-1918--Campaigns--Belgium--Ieper.
Ypres, 2nd Battle of, Ieper, Belgium, 1915.
Harvard subject headings:
Gases, Asphyxiating and poisonous--War use.
World War, 1914-1918--Campaigns--Belgium--Ieper.
Ypres, 2nd Battle of, Ieper, Belgium, 1915.
Princeton subject headings:
Gases, Asphyxiating and poisonous--War use.
Ypres, 2nd Battle of, Ieper, Belgium, 1915.