Coxsackie B-3 virus produces a mild infection which passes unnoticed in the non-hibernating Citellus lateralis. A severe infection occurs in the hibernating animal. The progress of infection in the hiberating animal is related to the number of arousal hours and quite independent of the number of infected days. Nevertheless, it has been shown that the low-temperature hibernation phase has a potentiating effect upon subsequent viral production. Infective virus has not been found in the inoculated brown fat pads during the hibernation phase but very high virus titers are recorded 48 hours after arousal. This results in an earlier viraemia and earlier and higher titers in other organs of the body. A similar effect is noted when virus is inoculated at the very beginning of the arousal phase. While most animals recover with subsequent antibody development, a few succumb. Antibody development is slow and related only to the number of arousal hours experienced.
Particular note is made of the fact that an animal may successfully resume hibernation despite complete loss of the axillary brown fat pads.
During preliminary studies it was observed that Citellus lateralis went into deep hibernation even when maintained in captivity. This animal proved to be susceptible to infection with Coxsackie B-3 virus both in the non-hibernating and the hibernating state (Dempster, Grodums and Spencer, '61). In the infected animal lesions were observed in the brain, heart, and brown fat tissues; other organs were not examined. Thus Citellus lateralis and Coxsackie B-3 virus provided a very satisfactory model for the further detailed study of the progress of a virus infection in a susceptible animal during various periods of the hibernators' life, both in and out of hibernation. Furthermore, it was hoped that since the brown fat tissue is acutely sensitive to damage by Coxsackie B-3 virus there might be an opportunity to test whether this tissue played a vital role in the hibernation cycle.
At a very early stage of these studies we wondered also whether the lipid composition of the brown fat would change in connection with the various seasons through which the hibernator passes, and how these changes would affect the susceptibility of the brown fat to the Coxsackie B-3 virus. It was observed, however, that within the limits of individual variations, the lipid composition in the brown fat was the