When oil is used in ketchup, it is easily detected under the microscope, as it appears in the form of shining, yellow globules which blacken gradually when treated with osmic acid. Besides this, the oil comes to the surface of the ketchup, where it can be seen readily, and if considerable oil has been used a distinct layer is formed. When the ketchup has been made for some time, the oil changes so that the ketchup has a peculiar “greasy” odor, or the oil may be so changed as to give a decidedly rancid smell to the ketchup. Oil usually causes a deterioration in flavor and odor, though some of the ketchups to which it has been added do not spoil readily. Olive oil, cottonseed oil, and oleomargarine are used. That the oil is not considered one of the regular known ingredients of the ketchup is shown by the failure to declare its presence on the label. To test the antiseptic value of oils in ketchup, experiments were made, using olive oil, cottonseed oil, and oleomargarine in the proportions of 1 part of oil to 1,000, 750, and 500 parts of ketchup, respectively. The ketchup was made in small quantities, 2 gallons for each experiment. After bottling, all except the check bottles were inoculated with Penicillium and kept at kitchen temperature. All spoiled, and neither the quantity nor kind of oil used had any marked effect in preventing spoilage. That the oils affected the development of the mold was evident. The mold developed first at the junction of the ketchup with the bottle forming a ring which spread gradually over the surface developing a somewhat heavy mycelium. This remained white longer than usual, spores forming very gradually, as indicated by the change in color from white to a delicate blue. At the end of three weeks only spots of color appeared on the surface and these were still blue, though in ordinary development the blue color changes to green in two or three days. Another test was made, using olive oil only, and in the proportions of 1 part of oil to 500, 400, and 300 parts, respectively, of the ketchup. Reduction was made in a steam-jacketed kettle, the oil being added when the ebullition of the ketchup was the strongest, after which the boiling was continued for fifteen minutes. The ketchup was bottled, unsterilized bottles being used, then covered loosely with the metal caps.