SULKIN AND ALLEN 



persistence of antibody and the occurrence of cyclic episodes of in- 

 fection in animals held at room temperature are incomplete at this 

 time. 



In the remaining sections of the figure, the shaded areas indicate 

 the periods following injection of virus when bats are maintained at 

 low temperature (10 *~^ C) and the influence of these periods of simu- 

 lated hibernation on the progress of infection has been plotted. When 

 animals are placed at 10° C immediately after inoculation, viral 

 multiplication is suppressed. Occasionally, one can demonstrate a 

 trace of virus in blood or brown fat, but it is difficult to determine 

 by assay of specimens in mice the fate of the virus inoculum during 

 this period in the cold. When the animals are transferred to room 

 temperature, virus reaches demonstrable levels in blood and brown 

 fat 2 to 3 days later. It appears that the infection which occurs 

 following a period of suppression in the cold is of shorter duration 

 than in room temperature groups, and antibody reaches significant 

 levels more rapidly. On the other hand, bats placed at 10° C one week 

 after virus inoculation, while at the peak of the infection cycle, 

 seem to suffer prolonged infection. Virus can be isolated regularly 

 from brown fat and blood for at least 30 days after the animals are 

 placed in the cold. Although subsequent data are incomplete, we 

 have included an instance in which virus was isolated from the brown 

 adipose tissue of a bat more than 2 months after the animal was 

 placed in simulated hibernation. The blood of this animal did not 

 contain demonstrable virus, but companion animals circulated virus 

 3 days after transfer to room temperature. None of the infected 

 bats developed antibody while in the cold, but plasma samples with 

 positive LNI were obtained from bats in this group approximately 2 

 weeks after transfer to room temperature. In still another series of 

 experiments mapped in the bottom section of Figure 3 we are 

 attempting to determine if an animal entering hibernation in an im- 

 mune state could, upon arousal, circulate virus again spontaneously. 

 Data along these lines accumulate slowly, since infected bats must 

 be held at room temperature 30 to 50 days for antibody develop- 

 ment, then withstand an additional month or more at 10° C and sur- 

 vive transfer back to room temperature before the end results can 

 be obtained. At the present time we have some data indicating that 

 at least some bats with positive LNI, when placed in the cold, lose 

 their antibody during a period of a month or more in hibernation 



386 



