a1 The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia
1. Two long-continued epidemics of mousepox were set up with different strains of the virus and maintained for 190 and 290 days respectively. Considerable differences were observed between the behaviour of the two strains of virus, the Moscow strain being much more virulent and more highly infective than the Hampstead strain.
2. The two strains of virus maintained their original characters through the experiments.
3. Life tables were constructed for both epidemics, specific and non-specific deaths being dealt with separately. They show that high and durable immunity follows recovery from infection.
4. Two mice which had recovered from infection were found to harbour small quantities of the virus in the lungs, and in one case in the spleen also, suggesting that chronic latent carriers of the virus may occur.
(Received August 31 1948)
* Francis Haley Research Fellow, Department of Experimental Medicine, University of Melbourne.