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Besides histamine another smooth muscle stimulating substance has been found in the nasal mucosa of dog and sheep. It is an acid which is readily oxidized by neutral aqueous potassium permanganate and osmium tetroxide, and is thermostable at pH 10.8 but not at pH 2.8. The purification of this acid has been followed by using the atropinized tortoise intestine as a test object, which is insensitive to acetylcholine, 5-hydroxytryptamine and small amounts of histamine. Both the tortoise intestine and rat colon are contracted by this acidic substance. The amount of histamine found in sheep nasal mucosa ranged from 12 to 23 mug./g. tissue and in dog nasal mucosa from 6 to 13 mug./g. tissue.