1. The intradermal method of inoculating Virus III, a hitherto unknown filterable virus producing lesions in rabbits, gives more reliable results than those obtained by smearing the virus on the scarified skin.
2. Virus III, heated 10 minutes at 55°C., will not produce visible reactions in the skin of rabbits.
3. Virus III passes through Berkefeld N and V filters.
4. The data obtained so far indicate that the best method of preserving Virus III in an active state is to filter the testicular emulsions containing the virus, add glycerol to the filtrate up to 40 per cent of the total volume, seal with vaseline, and store on ice.
5. Viable Virus III produces a definite immunity in rabbits which persists for at least 6 months. The immunity follows intradermal, intratesticular, intravenous, intracerebral, or intranasal inoculations of the virus.
6. A single intradermal injection of Virus III, which has been killed by heat, will not produce a demonstrable immunity in rabbits.
7. No passive immunity to Virus III could be demonstrated in rabbits which had received intravenous injections of 5 to 10 cc. of immune rabbit serum 24 hours previously.
8. Immune rabbit serum neutralizes Virus III either in vitro, or locally in a rabbit's skin when the immune serum and the virus are injected into the same part of the skin at or about the same time.
9. Three strains of the virus under investigation are immunologically identical.
10. Virus III and vaccine virus are immunologically distinct.
11. Virus III and the virus of symptomatic herpes are immunologically distinct.
12. No passive immunity to Virus III could be demonstrated in rabbits which had received intravenous injections of 5 to 10 cc. of serum or whole blood from patients convalescent from varicella.
13. Sera from two normal adults and from fourteen patients convalescent from varicella did not neutralize Virus III in vitro.
14. Rabbits could not be actively immunized against Virus III by injections of whole blood, vesicle fluid, or nasal washings from patients with varicella.
15. Four of twenty sera collected from stock rabbits of different ages, 20 per cent, neutralized Virus III in vitro. The animals whose sera neutralized Virus III failed to show a reaction at the site of intradermal inoculations with the same virus. About 15 per cent of 200 young stock rabbits (1,800 gm.) used in routine transfers were found to be refractory to Virus III, as evidenced by a failure to react to intradermal inoculations of the virus.
16. No susceptibility to Virus III was observed in guinea pigs, mice, or monkeys.
17. A volunteer who had never suffered from varicella experienced no general reaction and only a mild local one following an intradermal inoculation of Virus III. A volunteer who had had chicken-pox in childhood experienced a moderate general action, viz., fever, headache, backache, and general malaise, and also a moderate local reaction, viz., redness, swelling, tenderness, and pain, following an intradermal inoculation of Virus III.
18. The study of the immunological reactions has failed to bring any evidence that the virus under investigation bears an etiologic relationship to varicella.