Abstract
Summary
1. From 100 mice, orally infected with Col.SK virus at various times during the period of gestation, only 18 viable litters were obtained. These litters were equally divided among 25 surviving animals and 75 animals which succumbed to the disease.
2. The rate of abortion for mice inoculated during the first half of pregnancy, regardless of their capacity to resist infection, was high, being 72% for surviving animals and 88% for those which died, since two-thirds of the litters found in utero at the time of maternal death gave evidence of having predeceased the mother.
3. Fetuses obtained at autopsy consistently contained demonstrable amounts of virus.
4. Living young, when delivered at the time of onset of maternal symptoms, had apparently escaped infection, while a majority of stillborn young yielded virus.
5. Surviving offspring of susceptible mothers, born during the maternal incubation period, were apparently normal and usually escaped infection.
6. Litters of immune mothers, with one exception, were fully protected against intranasal infection between weaning and the age of 44 days. When tested between 66 and 68 days of age only 2 of 7 young were resistant, while after 119 days there was no evidence of immunity.
7. By means of experiments in which the offspring of immune and normal mice were interchanged during the period of suckling, immunity in the young was shown to be related to the observed immunity in the nursing mother.
8. Milk collected from normal mice contained no antiviral substances while milk from immune mice was capable of neutralizing the virus in vitro.
9. The data indicate that the protection of young mice is passive in nature and probably brought about by the ingestion of antiviral substances (antibodies?) in the milk of immune mothers. There is no evidence in this work to suggest that the offspring of infected mothers may acquire a state of active immunity through inapparent infection.
The author wishes to express her grateful appreciation to Mr. Anton Samuel for technical assistance in collecting milk from lactating mice.
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