An improved CO2 cabinet for low temperature storage of infectious agents with gaseous CO2 excluded from the specimen compartment.

The development of a low temperature storage cabinet for the preservation of viruses and other infectious agents some years ago (Horsfall, 1940) led to the use of similar solid C02 cabinets in numerous laboratories. The original cabinet has been in continuous operation for more than 11 years, and others more or less like it have been operating for almost as long. Despite the generally satisfactory results obtained by many workers with solid CO2 refrigerators of this kind, the use of the cabinet presents certain problems. Prominent among these are the following: (1) a decrease in the pH of unsealed specimens as a result of the absorption of gaseous C02, and (2) the cost of operation due to rapid consumption of solid CO2. Although a decrease in pH can be prevented by sealing specimens in glass or by the addition of an adequate buffer, neither practice is entirely satisfactory. Specimens sealed in glass are inconvenient to handle, and glass containers may break as a result of the marked temperature change (-i100 C) that occurs during rapid freezing or thawing. Buffers tend to fix the ionic environment of an agent in a manner that may preclude desired manipulation of this variable. Moreover, the addition of a buffer results in dilution of the infectious agent. The rate of consumption of solid CO2 can be reduced by increasing the efficiency of the insulation used and by decreasing the external temperature of the cabinet. However, to increase the thickness of the insulating material much beyond 6 inches causes the cabinet to become unwieldly and inconvenient. Moreover, to operate a CO2 cabinet in a closed cold room is dangerous for laboratory personnel unless adequate provision is made for exhausting from the room the large amounts of CO2 gas which evolve. With a view to overcoming the problems mentioned above, a solid C02 cabinet of markedly different design was developed in this laboratory 2 years ago. The cabinet has been in continuous operation during this period and has proved entirely satisfactory. Certain novel features in design contribute to the advantages of the improved cabinet: (1) gaseous CO2 is entirely excluded from the specimen cabinet, and, as a consequence, no change in the pH of unsealed and unbuffered specimens occurs; (2) the cabinet operates in a closed cold room held at a temperature of 4 C and, as a result, the consumption of solid C02 is less than half what it would otherwise be; (3) all gaseous C02 from the refrigerant bunkers is exhausted outside the cold room, and there is therefore no personnel hazard from operating the cabinet in a closed space. Desin of the cabinet. The details of the design of the cabinet' are shown in