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Antibiotic Zone Reader (Fisher-Lilly)

Mount Sinai Pathology Lab · Health Sciences

A black metal instrument with a roughly rectangular footprint. On the sides of the instrument, near the front, are two large linked wheels, one of which has increment marks around its circumference. Turning these wheels moves a wide belt that covers most of the top surface of the instrument. The increments on the wheel indicates the movement of the belt

Attached to this belt is a shallow metal circular platform that is intended to support a Petri dish of ~9.5cm in diameter. Part of this platform has been cut away to reveal a lens. Beneath this lens, within the body of the instrument, is an electric light. Rotating a Petri dish within this platform will illuminate an area of its perimeter. Moving the belt using the wheels will move the entire dish relative to the illuminator. A switch near the rear of the right side of the instrument operates the illuminator. An electrical cord extends from the rear of the instrument.

A metal stem extends from the rear of the top surface of the instrument to point ~5cm above the illuminator. This contains an optical arrangement that projects an image of the surface of a dish, located directly below it, onto a prism located at the top-front of the instrument. The user observes the surface of the Petri dish by looking downwards into the long face of the right triangular prism.

Accession Number: 2022.MTS.1

Alternative Name:

Primary Materials: Iron Alloy, Glass


The metal manufacturer’s label riveted to the front of the instrument includes the following information: “115 VOLTS 50/60 CYCLES A.C. ONLY”// “PATENT APPLIED FOR”.

Dimensions (cm): Height = 20, Width = 30, Length= 34


This instrument is used to gauge the effectiveness of antibiotics against a given strain of bacteria.

In order to use it, a Petri dish is inoculated with bacteria, which is permitted to grow over its surface. Disks of antibiotics are placed at regular intervals near the perimeter of the surface of the dish. This instrument is used to accurately measure the diameter of the “inhibited zone” created by each antibiotic disk, that is, size of the area of bacteria that the antibiotic disc has killed.


This instrument is well worn. The finish on the advance wheels is corroded. The advance mechanism appears to work. The instrument was not tested to determine whether the illuminator is in working condition. The prism at the front of the instrument has become detached. There are four small patches of missing black crinkle finish on the front face of the stem above the Petri dish holder.

Associated Instruments:


Fisher Scientific Co. (Pittsburgh, New York, St. Louis, Washington, Montreal); “Manufactured in U.S.A. …”

Date of Manufacture: c. 1950s


The Mount Sinai Pathology Lab collection was transferred from a display case on the 6th floor of Mount Sinai Hospital (600 University Ave. Toronto, On) over several days in mid-December 2020.

Additional Information and References:

Fisher Scientific co. “for Standardizing Bio-assays FISHER-LILLY Antibiotic Zone Reader” Archives of Pathology 1951-09: Vol 52 Iss 3, p.4. (Digitized by Internet Archive, accessed November 26, 2022)

Historical Notes:

This instrument exists in many variations, including recent forms with various levels of automation. The indication “patent applied for” on the manufacturer’s label indicates that this model may be the earliest version.

  • Donated to UTSIC