The Effect of Dispersal during the Pre-epidemic Stage, and of subsequent Re-aggregation

If a mouse-population, which has been exposed to the risk of infection, be dispersed into several small groups during the pre-epidemic stage, the total mortality will be far less than if the animals be retained as a single large group. The specific mortality will be reduced to a still greater extent. 2. During the period of dispersal, the mice forming the small groups will, in most cases, have passed through an extended pre-epidemic phase of the spread of infection. In so doing they will have acquired an appreciable degree of immunity. 3. If the small groups be later re-combined into a single aggregate, further deaths will occur; but the total mortality among a group of mice, which has been dispersed and then re-accumulated, will always be less than among a similar group, which has been retained from the commencement as a single unit of population. The specific mortality will generally show a still greater reduction. It remains for me again to express my thanks to my colleagues, Dr H. B. Weir and Dr G. S. Wilson, for their assistance in this investigation.