McIntosh and Fildes’ Anaerobic Jar Principle, Procedure


Table of Contents

McIntosh and Fildes’s anaerobic jar is a tool utilized in microbiology laboratories, to generate anaerobic circumstances (anaerobiosis) to cultivate obligate anaerobes, such as Clostridium spp. Anaerobiosis derived from McIntosh and Fildes anaerobic jar is among the most effective and most frequently employed methods for anaerobiosis however it requires expensive special equipment and a vacuum pump. Gas supply availability is another drawback to this technique. It is currently being replaced with an easier GasPak system.

About McIntosh and Fildes’ Anaerobic Jar

McIntosh and Fildes’ jar comprises of an 8*5 inches (20*12.5 cm) glass jar made of strong glass or stainless steel with a secure fit lid of metal. The lid is clamped in airtightness using a screw. It is equipped with two tubes that have taps. One is for the inlet of gas inside (inlet) and one for outlet for a vacuum valve. The lid is also equipped with two terminals that are connected to an electric source. Alumina pellets in a capsule that are coated in palladium (palladinished Alumina) is suspended beneath the lid using strong wires that connect to terminals in order to heat the catalyst to activate it. Nowadays, catalyst active at room temperature is also available.


Principle of McIntosh and Fildes’ Anaerobic Jar

McIntosh and Fildes anaerobic jar works according to the concept of replacement and evacuation, in which the air within the chamber is ejected and replaced with a mixture made of gas (consisting of 5% CO2, 10% H2 and 85% N2) .

It is almost impossible to eliminate all the air, so a small quantity of oxygen will remain. The remaining oxygen can be converted into water with the help of Spongy platinum catalyst or palladium. The catalyst functions as a catalyzing agent , causing slow synthesis of oxygen and hydrogen to create water. Reduced methylene blue can be used to indicate (mixture from NaOH methyleneblue, along with glucose). It turns colorless when it is inaerobically treated, but it regains its blue color upon contact with oxygen.



  1. Keep the culture plates inoculated inside the jar , along and an indication.
  2. Secure the lid by screwing it on.
  3. Shut off the inlet tube and connect the outlet tube to the vacuum pump ( at least three quarters of air inside the jar could be taken away).
  4. Take note of the pressure on a vacuum gauze. When the pressure drops to 100mmHg (i.e. 600 millimetres below atmospheric) make sure to tightly shut your outlet faucet.
  5. Connect the inlet tap to a hydrogen source and then, open it. Hydrogen is then pumped through a small bottle to wash.
  6. Increase the pressure to 760 mg Hg (i.e. atmospheric) by monitoring the gauze vacuum as zero.
  7. The electric terminals are switched on to heat the crystal (When the catalyst is at room temperature, used , no heating is required).
  8. The catalyst aids in the fusion of residual oxygen and hydrogen to produce water. The process can last for about 20 minutes.
  9. Let the McIntosh and Fildes Jar in an incubator set at 37°C for 48 hours.

Monitoring efficacy of anaerobiosis

Reduced methylene blue indicator can be utilized to determine the efficacy of anaerobiasis. A tube that contained reduced methylene blue solutions had to be kept in the jar, along with the plates for culture. Methylene blue appears colorless under reduced conditions , and it changes to blue when it is oxidized.

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