The experiments, an account of which is given here, were based on two sets of observations—a personal one and one recorded by Zinsser and Seastone (1930). The personal observation relates to the injurious action of air on the virus of herpes. The method in common use for the preservation of this virus consists in the cold storage of pieces of infective brain in glycerol—pure or diluted. If special precautions are taken to exclude air, material so preserved will retain its infectivity for several years. In an ice chest with an average temperature of + 9° C. it has been my experience that unless air is largely excluded (
e. g
., by a layer of liquid paraffin) the brain will cease to be infective after a period of 3 to 4 months. Under a layer of liquid paraffin and at that temperature the material will still be infective after 2 years. Cold storage at lower temperatures yields better results under both aerobic and anaerobic conditions. The acidity which develops when pieces of fresh tissue are preserved in glycerol has apparently little injurious effect on the virus. The second observation is that of Zinsser and Seastone, who found that a filtrate of herpes virus which possessed a low degree of infectivity and took as much as 11 days to kill a rabbit on cerebral inoculation, recovered its infectivity to such an extent after the addition of cysteine that the incubation period was reduced to 5 days. In a second and more striking experiment an active filtrate of herpes virus lost its infectivity for the rabbit by simple exposure to air for 8 days at room temperature, yet the inactive sample recovered its full infectivity by the addition of cysteine and anaerobic preservation for a further 17 days. Since these observations suggest that exposure to air tends to inactivate the virus of herpes and that the inactivated virus can be reactivated under conditions which favour an increase in the reduction potential, an attempt was made at inactivating broth filtrates of this virus by saturation with oxygen and subsequent reactivation by a process of reduction.
Filtrate
.—Only broth filtrates obtained from diffusates were used. The diffusates were prepared as follows. The cerebral hemispheres of a rabbit which had been killed at the height of a typical attack of herpetic encephalitis, were roughly crushed
in situ
with a pair of dissecting forceps and dropped into a tube containing 30 c. c. of Hartley’s broth over which a layer of liquid paraffin was floated. The tube was left at room temperature for a few days (5-10) and then was transferred to the cold room until required. Such diffusates will be found active even 18 months later and are easily filtered. After centrifuging the diffusate was filtered through a Pasteur-Chamberland L2 or L3 candle at a negative pressure of 20 cm. Hg. As the filtrate obtained from the first candleful of the diffusate was frequently found to be inactive, it was usually rejected. The rest of the filtrate, unless used immediately, was sealed with vaseline and kept in the cold.
Design and construction of a cold room with photovoltaic support for lighting
