A series of organic sulphides from the ethereal oil had a strong blood sugar reducing property. The pure sulphide had only a slight action or none. A fall in blood sugar was obtained in rabbits and depan-creatized dogs after garlic extracts by mouth. The active principle is steam volatile and ether-soluble. A blood sugar raising principle is also present. No toxic symptoms are observed except by very large doses. A white crystalline product, with a sharp melting point (174[degree]), sulfur-free and with characteristic alkaloidal precipitation and color reactions, was isolated. Sulfur is present in the active fraction. Both S and the alkaloid are necessary for the activity,* neither itself is active. Combining the 2 causes a slight fall in blood sugar.