Abstract
In preliminary work it was found that age was an important factor in the resistance of ordinary white mice to the influenza virus. Animals 4 to 6 weeks of age died regularly between 3 to 6 days after 0.05 cc of a 5% influenza filtrate was instilled into their nostrils. Older animals survived the same treatment for longer periods, in some cases as long as 17 days. Studies were outlined in an attempt to learn the effect of heat, cold, fatigue, and alcohol upon the resistance of mice to the virus. However, in early experiments it was found that old animals did not tolerate heat, cold and fatigue; therefore, 4- to 6-weeks-old mice were regularly employed.
The inoculum consisted of 0.05 cc of a 1:100,000 dilution of mouse lung tissue infected with the PR8 strain of influenza virus. It was prepared by grinding a 5% tissue suspension in broth of pH 7.2, centrifugating at 1600 rpm for 10 minutes and then passing the supernatant fluid through a Berkefeld N filter at a negative pressure of 50 cm of mercury. Many experiments were carried out, but only the following will be given since the findings were constant in; each instance.
Heat. A group of 9 mice was “hot-room” treated as follows: 6 were inoculated with the virus; the remaining 3 were used as controls. One-half hour after the inoculation, all the animals were placed in the hot room at 37°C and a relative humidity of 100%, for 24 hours. They were transferred to room temperature, 18°C, for 20 hours and then returned to the hot room for 10 hours. This completed the “hot-room” treatment. The animals were sacrificed' and autopsied at the end of the fifth day.
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